i have always thought that adults should be able to do basic math in their heads to a degree. when you are purchasing less than 10 items it isnt hard to add them all up. when its a grocery trip then that is harder. still you can keep a rough tabulation going and compare the cashiers total to what you would estimate it.
Frankly there are a lot of people who dont pay attention to what they are buying. i used to see parents grab or let their kids grab anything from thr hospital cafeteria without looking at the prices. then the parents would go ballistic when their meal turned out to be $25-40
I ended up disputing the total of two flash drives and a coke that i bought from Staples last week. the cashier read back the total, whic was about 5 bucks more than expected. when i questioned the cashier she said that one drive was more than the other. i told her both were the same sale price. she then told me that one of the drives that i hadpicked out of the sale bin was in fact not on sale and was regular price. so i ended up shelling out for the non sale drive since it was a gift for the gf.