The simplest point of sale equipment

Two secure smart cards.  Have the clerk one of the company clerk cards.  The clerk keeps it in the cash register. Customer pays company with paper cash or secure card.  If it is secure card, the transaction is exactly the same, almost. The clerk pulls out the company card, and taps the exchange with the customer card, then puts the store card back into the register. Almost exactly like taking paper cash.

At the end of the shift, clerk takes cash box to office, just as always.  The cash runs through the cash counter machine, the card taps the company computer.So, peer to peer exchange drops the POS expense cost to $50, about a tenth the cost of the cash register.