The order changes the answer
Discount then tax, or tax then discount? It sounds like a nitpick, but the two paths land on different totals. Applying the discount first, so tax only lands on the amount the customer actually pays, is how nearly every quote and receipt is built.
Getting it backward tends to overcharge, and customers who spot it aren't shy about saying so. This tool locks in the standard order so your numbers match what people expect to see.