Personally and professionally I am on and been on both sides.
Let's say you find a ham on sale for 58 cents/lb while doing some strolling shopping (this past Friday at Hannaford). Sign posted with the name. You like ham and want to take advantage of this find. That 8/lb ham rings up at $15.92 instead of $4.68. I'm stopping the line for a price check or canceling my order and going to the service desk. I'll walk an associate to the sign to justify my $5 ham.
It is the responsibility of whoever and not the cashier, to satisfy me. How many other items and how many other customers are getting overcharged? You may very well be a person on line behind me with the same overcharge. That's not fair to you either. This grocer needs to get their act together. They will will lose my and your business. You will eventually catch on to their lack of management of prices.
Coupons are a part of marketing. If I have a fist full of coupons that gets me $100 worth of groceries for 10 bucks then I am a smart shopper. Tough shit that you are on my line. I got there first. Wait 2 minutes for someone to save 90%. Yea, I've been behind people that shovel a hundred coupons only for mast of them to be expired or other bullshit. They are nickle squeezing inconsiderate pigs. But if think that you should be the first in line ANYWHERE be it at the grocery, bodega, bank, etc. and you deserve priority service then go fuck yourself. Traffic doesn't always cater to your desires.