And what happens when the battery runs out, or the power fails?
I was in a major drugstore several months ago. The computerized cashregister went up and the clerks stopped making sales. The damned store shut down.
Needless to say, I've never gone back.
You want a real kick? Buy something for $4.77 and give the clerk $5.02 to pay for it. Watch in amazement as the clerk is initially confused by the two cents and then realizes (after the cash register does the math) that you magically get a quarter back. Just how are people able to do that?