There are two approach of discount.

1. Discount after taxes. Apply discount after taxes. For example, product price is $100, the tax is 13% and the discount is 10%, so this approach will result (100 * (100 + 13) / 100) – (100 * 10 / 100) = 103.
2. Discount before taxes. Apply discount before taxes. For example, product price is $100, the tax is 13% and the discount is 10%, so this approach will result (100 – (100 * 10/100)) * (100 + 13) / 100  = 101.7.

Most of businesses choose the approach (1) including large businesses, so MiniPOS implements the approach (1) by default. If you want to choose the approach (2), you can follow the steps as below.