CET-510/fix: Fix magento calculations

At present, we derive the gross amount for line item. This is causing rounding error in some cases.
Instead we should use gross amount provided by magento

Service/Order.php

@@ -226,6 +226,7 @@ public function getProductImageUrl(Product $product): string
      *
      * @param mixed $amt
      * @param int $dp
+     *
      * @return string
      */
     public function roundAmt($amt, $dp = 2): string
@@ -234,77 +235,81 @@ public function roundAmt($amt, $dp = 2): string
     }
 
     /**
+     * Get gross amount (inclusive of tax after discount)
+     *
      * @param OrderItem|InvoiceItem|CreditmemoItem $item
+     *
      * @return float
      */
     public function getGrossAmountItem($item): float
     {
-        return $this->getNetAmountItem($item) + $this->roundAmt($this->getTaxAmountItem($item));
-    }
+        return $this->getNetAmountItem($item) + $this->getTaxAmountItem($item);
 
-    /**
-     * @param OrderItem|InvoiceItem|CreditmemoItem $item
-     * @return float
-     */
-    public function getNetAmountItem($item): float
-    {
-        return $this->getNetAmountBeforeDiscountItem($item) - $this->getDiscountAmountItem($item);
     }
 
     /**
+     *  Get net amount (exclusive of tax after discount)
+     *
      * @param OrderItem|InvoiceItem|CreditmemoItem $item
      * @return float
      */
-    public function getNetAmountBeforeDiscountItem($item): float
+    public function getNetAmountItem($item): float
     {
-        return (float)$item->getRowTotalInclTax() / (1 + $this->getTaxRateItem($item));
+        return (float)$item->getRowTotal() - $this->getDiscountAmountItem($item);
     }
 
     /**
+     * Get unit price
+     *
      * @param OrderItem|InvoiceItem|CreditmemoItem $item
+     *
      * @return float
      */
     public function getUnitPriceItem($item): float
     {
-        return $this->getNetAmountBeforeDiscountItem($item) / $item->getQtyOrdered();
+        // $item->getRowTotal() is before discount
+        return (float)$item->getRowTotal() / (float)$item->getQtyOrdered();
     }
 
     /**
      * @param OrderItem|InvoiceItem|CreditmemoItem $item
+     *
      * @return float
      */
     public function getTaxRateItem($item): float
     {
-        return $item->getTaxPercent() / 100;
+        return (float)$item->getTaxPercent() / 100;
     }
 
     /**
+     * Get tax amount inclusive of discount
+     *
      * @param OrderItem|InvoiceItem|CreditmemoItem $item
+     *
      * @return float
      */
     public function getTaxAmountItem($item): float
     {
-        return $this->getNetAmountItem($item) * $this->getTaxRateItem($item);
+        return (float)$item->getTaxAmount();
     }
 
     /**
+     * Get discount amount before tax
+     *
      * @param OrderItem|InvoiceItem|CreditmemoItem $item
+     *
      * @return float
      */
     public function getDiscountAmountItem($item): float
     {
-        $discount = abs((float)$item->getDiscountAmount());
-        $discountTaxCompensation = abs((float)$item->getDiscountTaxCompensationAmount());
-        if ($discountTaxCompensation > 0) {
-            $discountTaxCompensation = $discount * (1 - 1 / (1 + $this->getTaxRateItem($item)));
-        }
-        return $discount - $discountTaxCompensation;
+        return (float)$item->getDiscountAmount() - (float)$item->getDiscountTaxCompensationAmount();
     }
 
     /**
      * Get category array by category ids
      *
      * @param array $categoryIds
+     *
      * @return array
      * @throws LocalizedException
      */
@@ -324,7 +329,9 @@ public function getCategories(array $categoryIds): array
 
     /**
      * Get category collection
-     * @param $categoryIds
+     *
+     * @param array $categoryIds
+     *
      * @return Collection
      */
     private function getCategoryCollection($categoryIds): Collection