Ooh, brainstorm.  Why bother scanning everything individually?  Give every product an RFID tag, shop by putting things directly into your bag and then have "scan out" stations.  These stations would be just putting all your stuff down, it checking what RFIDs were in the scanning area and you tapping your phone for the crypto payment.  On exit you'd pass through detectors like most stores have now that would detect RFIDs that haven't been paid for.

Also, the short lag between scanning, tapping, and blockchain verification would be perfect for completing a small in-store survey at the scan station.