To the OP: I would have the same reaction. If what I put on the register was not enough, I would not be in the line checking out, would I? I understand in some cases, it is a matter of being courteous, however, I would probably select a better comment (e.g., thank you for shopping at our store, or something along those lines). The other comment that grinds my gears is "Did you find everything you needed today?" Again, if I didn't, I would have brought it to the attention of a manager before checking out.
LOL, exactly Vg7405, great minds