I heard of this policy decades ago, when scanners were new, and people were suspicious. Like many people have already said, I don't think it was a law. It always struck me as something to placate technophobics, and having watched too much Star Treck, don't include myself in that group.
BS like this can happen. Back in my high school days, when I worked at the supermarket(this was just as scanners were arriving), the office lady had to enter codes from printouts by hand, and mistakes do happen.
My solution is to never buy more than a handfull of items at a time, so I can better see what's happening. That policy works well if you're a bachelor, or European.
And I also like to use the self-serve scanners. People hate them , tending to complain about the loss of human contact. I'm not so lacking in human contact that I have to make chitchat with the lady at the register.
