I respect your preference, and for some people it could even be considered a “reasonable accommodation.”

But I prefer to have the person who does this all day whip through the scanning and bagging while I pay up. It may not be rocket surgery, but good cashiers have an efficiency of eye/brain/hand motion that I can’t match. Especially when there’s multiples of the same item, their machine trusts them to do it the efficient way rather than scanning and weighing each item. Or having the produce codes at their fingertips without stopping to read them. And since all machines have little quirks, it’s helpful to know exactly where to apply “percussive maintenance.”

Having both options is best and should be part of ADA compliance.