A security camera on the register seems like the easiest way. If the cashier’s count doesn’t match the sum of customer transaction then watch the footage until you see them pocket the money.
At larger companies they absolutely do this. And the digital video is stored with an overlay of what is ringing up with it's price as the cashier scans it. So it is easy to see if they are not scanning items for a partner or manually entering the wrong barcode.
Thus proving you don't need the manager oversight ?
Monitoring with cameras seems like an advance in technology that lowers the need for managers in the room.
But it’s still a check as advocated earlier in the thread.