I have an idea. All the store needs is a sign with a QR code.

When a bitcoin freak scans the QR code, the freak is taken to the Strike tipping page like https://strike.me/odell/

It says Tips, but it can be used as a POS. Say you owe your bartender or dry cleaner $21.00.

Simply scan the QR code. Enter $21.00. Pay the invoice. 

The merchant gets paid in sats or fiat. It can work at your local coffee shop or Wendy's. Nor does it require training employees how to accept bitcoin.