An obvious question?

At Smiths (I can't vouch for other stores... I shop almost exclusively at Smiths these days. Sorry Macey's), when you check out and are ready to pay, you slide your credit card, and then a screen pops up on the credit card sliding machine that says:

$20.08
Is this ok?
Yes       No

And you're supposed to hit Yes to continue. But every single time it does I look at what I bought and then look at the amount and think "you know, actually, if you really are asking, $20.08 seems a little high. How about $12.83?? That seems much more reasonable."

But of course they really do want the full $20.08 for my fruits, vegetables, yogurts and meat and sugar and chocolate and two containers of ice cream.

Why are they asking if they don't even care??!!!