I have checked below mentioned files to override tax functionality.

\vendor\magento\module-tax\Model\Sales\Total\Quote\Tax.php

\vendor\magento\module-tax\Model\Sales\Total\Quote\CommonTaxCollector.php

I am looking into mapItem function in CommonTaxCollector.php. I have added static value for setBaseTaxCalculationPrice and setTaxCalculationPrice but cart row total, subtotal and tax are changed.

I want to change only tax to apply it on manufacturer cost instead of price. Row total and Total should not be affected.

public function mapItem( \Magento\Tax\Api\Data\QuoteDetailsItemInterfaceFactory $ itemDataObjectFactory, AbstractItem $ item, $ priceIncludesTax, $ useBaseCurrency, $ parentCode = null ) { $ writer = new \Zend\Log\Writer\Stream(BP . ‘/var/log/mylogfile3.log’); $ logger = new \Zend\Log\Logger(); $ logger->addWriter($ writer); $ logger->info($ item->getTaxCalculationPrice());

    if (!$  item->getTaxCalculationItemId()) {         $  sequence = 'sequence-' . $  this->getNextIncrement();         $  item->setTaxCalculationItemId($  sequence);     }     /** @var \Magento\Tax\Api\Data\QuoteDetailsItemInterface $  itemDataObject */     $  itemDataObject = $  itemDataObjectFactory->create();     $  itemDataObject->setCode($  item->getTaxCalculationItemId())         ->setQuantity($  item->getQty())         ->setTaxClassKey(             $  this->taxClassKeyDataObjectFactory->create()                 ->setType(TaxClassKeyInterface::TYPE_ID)                 ->setValue($  item->getProduct()->getTaxClassId())         )         ->setIsTaxIncluded($  priceIncludesTax)         ->setType(self::ITEM_TYPE_PRODUCT);      if ($  useBaseCurrency) {         if (!$  item->getBaseTaxCalculationPrice()) {             //$  item->setBaseTaxCalculationPrice($  item->getBaseCalculationPriceOriginal()); 

$ item->setBaseTaxCalculationPrice(‘200’);

        } 

$ itemDataObject->setUnitPrice($ item->getBaseCalculationPriceOriginal()) ->setDiscountAmount($ item->getBaseDiscountAmount());

    } else {         if (!$  item->getTaxCalculationPrice()) {            //$  item->setTaxCalculationPrice($  item->getCalculationPriceOriginal()); 

$ item->setTaxCalculationPrice(‘200’);

        } 

$ itemDataObject->setUnitPrice($ item->getBaseCalculationPriceOriginal()) ->setDiscountAmount($ item->getDiscountAmount());

    }      $  itemDataObject->setParentCode($  parentCode);      return $  itemDataObject; }