It really does boggle the mind that this isn’t a given.

What benefit is there to NOT having a cashier sit? That’s a serious question I’m assuming there’s got to be some reason I’m not aware of.

I’ve been told over and over that it looks “professional” to be standing.

Is it more professional to have a grimace on your face and a short temper because your whole body aches from standing for six hours?

Apparently. We also get yelled at for leaning. “If you have time to lean you have time to clean” is a thing.
Like excuse me for leaning on my register for 1 minute to take pressure off my lower back.

All that’s been said is 100% TRUE! I am a cashier at a McDonalds for the bloody ass drive thru. My feet and knees are screaming for me to sit after i get off work at 3 (i work 7-3, Monday-Friday).so, whenever i get off work, i try to go straight home, and just sit all night. They also get onto us saying that if we can lean against the wall for more then a few seconds, we can be doing something else instead.  Luckily, the break room is right across from me, so i can sneak into there and snag a chair so long as no ones in the drive thru.