Yes, several models (e.g. Vx570) have a USB port which can accept an external keyboard, to which you'd attach a keyboard-wedge 2d barcode scanner that supports QR codes.

Having the credit card terminal approve and sign transactions sent by a computer (either via RS232 or USB) is also a very useful application.  (When connected to a computer, it will look like a serial port over USB, as it supports serial port emulation).