POS systems don't do the bank interface anymore ... usually it is a piece of middleware sits on the POS that is used to control the actual interface to the bank

POS systems don't do the bank interface anymore ... usually it is a piece of middleware sits on the POS that is used to control the actual interface to the bank and the PED (swipe devices). POS says I need payment to the value of amount ... middleware takes over and the POS get's back the card number encrypted (PCI) , auth code and cryptogram if chip (EMV) was used. Loyalty programs are a different matter altogether , full itemization is sent to the third party if you are enrolled in a program.