**If you have Taxes included in the Price of the product (e.g. for most European customers), then it is removed when calculating Gross Sales (and therefore, Net Sales).
This is because otherwise, Taxes would be counted twice when taxes are added back in to work out Total Sales.
For example, imagine 2 units of a product sold for 100.00 and a tax of 12% was included in that price.
Price minus tax: 100 / 1.12 = 89.29, so Gross Sales = 2x 89.29 = 178.57
Then if a discount of 50% was applied = 178.57 x 0.5 = 89.29
And now if one unit was returned, we'd have the other still = 44.64 in Net Sales
Finally, you would add the taxes back in (12% of the net sales is 44.64 x 0.12 = 5.36), plus a Shipping Charge of 5.00, and we get Total Sales of 55.00