A $50 tablet with something like BitPay and LN on it + a new tag on the POS system to label BTC payments on USD transactions. Customer pays with Bitcoin via tablet. Staff enters transaction and $ value at that time into the till to account for the lack of paper money and then you cash-off your tills like you always would only that you'd add the BTC transactions of the day to your card and cash payments.

Sounds more complicated than it is.