Veggies are most likely weighed on a scale tied in with over all charging mechanism. IOW, you put a bunch of bananas on the scale and the screen asks you to select the itmes name from a list or a picture and then applies the proper per pound price for that item and adds it to your total. This is now done in stores which have self check out.
Just like current self-checkouts, which are nice but usually screws up with veggies.