Idiot Cashiers

What is it with these moronic cashiers these days. Several times over the last few weeks I have encountered these idiots with absolutely no common sense or math skills. They should definitely not be allowed to operate a machine that handles money. A lot of times if the amount that I owe is somewhere around $6.75, I will give them 12 dollars in hopes that I can get a 5 dollar bill back, instead of a bunch of ones which I can't stand. A move like this will completely baffle the 16-year-old behind the counter. They look at me like I have the fucking plague. They stare at the 10 and 2 ones that I give them for a good 30 seconds, then they give me back 2 dollars like I'm the fuckin moron. All you have to do is type in $12.00 in your little register and it should be pretty clear that I am getting back $5.25. Don't overthink it. Just type in 12 and then maybe the little light will go on in your head. Sometimes I try and explain to them what I am trying to do here, but most of the time it is a lost cause. They think I am somehow trying to rip them off by asking for a 5 or a 10 back for my change.
I am to the point where I don't even want to argue with these people anymore. I guess I will just have to resort to carrying around a pocket full of ones fatting my wallet as I try and make purchases. Maybe someday I will have enough ones to pay for something with only those. It would make life much easier for these dolts who can't figure out some simple math.