For the person that sacks my groceries, that's all they do, maybe an occasional price check, but for the most part there is no required skill set. Don't put the chicken with the beef. Cold stuff goes together and heavy stuff goes on bottom. All that is in a 30 minute orientation video and the majority of the kids still can't do it right. Why should they make more than $7.25/hr?
If you can sack my groceries correctly, repeatedly, you will get noticed and become a cashier. Maybe you get a raise, and you don't lose money out of your till so they make you a manager on the front end, you get another raise. And so on and so on.
My point is, I don't see the need to pay people more for crappy service, which is what 99 percent of minimum wage employees give.