When you have a lot of customer in front of the cashier you just want to type the price you want them to pay.
Example: I sell for 30 € to a loyal customer; I usually give him 15% discount.. so the price is 25,5€. But I tell him: <<just give me 25€>>.
I know I can set the discount directly in euros, but a POS is a winning solution if you can type as quickly as possible (even when your employes have no "skills";-)
I think that for a "computer" do this calculus (add this feature) is really simple.
Let me know;-)