I have added discount from a custom module that i made.I am giving the observer’s code below.Its working fine on the Cart page but tax is not getting added on Checkout Page. Getting paypal error: “PayPal gateway has rejected request. The totals of the cart item amounts do not match order amounts (#10413: Transaction refused because of an invalid argument. See additional error messages for details).” during checkout.

class Hs_Customcartdiscount_Model_Observer {  const XML_PATH_MODULE_ENABLE    = 'customcartdiscount/customcartdiscount_group/enable'; const XML_PATH_DISCOUNT_AMOUNT  = 'customcartdiscount/customcartdiscount_group/discount';  public function setDiscount($  observer) {     if(Mage::getStoreConfig(self::XML_PATH_MODULE_ENABLE)){         $  quote = $  observer->getEvent()->getQuote();         $  quoteid = $  quote->getId();         $  discountAmount =floor($  quote->getBaseSubtotal()/100) * Mage::getStoreConfig(self::XML_PATH_DISCOUNT_AMOUNT);         if ($  quoteid) {             if ($  discountAmount > 0) {                 $  total = $  quote->getBaseSubtotal();                 $  quote->setSubtotal(0);                 $  quote->setBaseSubtotal(0);                  $  quote->setSubtotalWithDiscount(0);                 $  quote->setBaseSubtotalWithDiscount(0);                  $  quote->setGrandTotal(0);                 $  quote->setBaseGrandTotal(0);                   $  canAddItems = $  quote->isVirtual() ? ('billing') : ('shipping');                 foreach ($  quote->getAllAddresses() as $  address) {                      $  address->setSubtotal(0);                     $  address->setBaseSubtotal(0);                      $  address->setGrandTotal(0);                     $  address->setBaseGrandTotal(0);                      $  address->collectTotals();                      $  quote->setSubtotal((float) $  quote->getSubtotal() + $  address->getSubtotal());                     $  quote->setBaseSubtotal((float) $  quote->getBaseSubtotal() + $  address->getBaseSubtotal());                      $  quote->setSubtotalWithDiscount(                             (float) $  quote->getSubtotalWithDiscount() + $  address->getSubtotalWithDiscount()                     );                     $  quote->setBaseSubtotalWithDiscount(                             (float) $  quote->getBaseSubtotalWithDiscount() + $  address->getBaseSubtotalWithDiscount()                     );                      $  quote->setGrandTotal((float) $  quote->getGrandTotal() + $  address->getGrandTotal());                     $  quote->setBaseGrandTotal((float) $  quote->getBaseGrandTotal() + $  address->getBaseGrandTotal());                      $  quote->save();                      $  quote->setGrandTotal($  quote->getBaseSubtotal() - $  discountAmount)                             ->setBaseGrandTotal($  quote->getBaseSubtotal() - $  discountAmount)                             ->setSubtotalWithDiscount($  quote->getBaseSubtotal() - $  discountAmount)                             ->setBaseSubtotalWithDiscount($  quote->getBaseSubtotal() - $  discountAmount)                             ->save();                       if ($  address->getAddressType() == $  canAddItems) {                         //echo $  address->setDiscountAmount; exit;                         $  address->setSubtotalWithDiscount((float) $  address->getSubtotalWithDiscount() - $  discountAmount);                         $  address->setGrandTotal((float) $  address->getGrandTotal() - $  discountAmount);                         $  address->setBaseSubtotalWithDiscount((float) $  address->getBaseSubtotalWithDiscount() - $  discountAmount);                         $  address->setBaseGrandTotal((float) $  address->getBaseGrandTotal() - $  discountAmount);                         if ($  address->getDiscountDescription()) {                             $  address->setDiscountAmount(-($  address->getDiscountAmount() - $  discountAmount));                             $  address->setDiscountDescription($  address->getDiscountDescription() . ', Custom Discount');                             $  address->setBaseDiscountAmount(-($  address->getBaseDiscountAmount() - $  discountAmount));                         } else {                             $  address->setDiscountAmount(-($  discountAmount));                             $  address->setDiscountDescription('Custom Discount');                             $  address->setBaseDiscountAmount(-($  discountAmount));                         }                         $  address->save();                     }//end: if                 } //end: foreach                 //echo $  quote->getGrandTotal();                  foreach ($  quote->getAllItems() as $  item) {                     //We apply discount amount based on the ratio between the GrandTotal and the RowTotal                     $  rat = $  item->getPriceInclTax() / $  total;                     $  ratdisc = $  discountAmount * $  rat;                     $  item->setDiscountAmount(($  item->getDiscountAmount() + $  ratdisc) * $  item->getQty());                     $  item->setBaseDiscountAmount(($  item->getBaseDiscountAmount() + $  ratdisc) * $  item->getQty())->save();                 }             }         }     } } 

}

two screenshots of cart page and checkout page: cart page checkout page

Please someone help me.