Massachusetts regulation addresses this particular misincentive with a "one item (per customer day) is $10 off" when a food store/department scanner/checkout price isn't the lowest of advertised/display/sticker/scanner price. My own supermarket experience is of a clear sign posted by the cashier, and of hassle varying from the cashier handling it routinely and quickly, to trick question "So you want ${scanned - correct} back?", to waiting for a manager type and initialing/signing something simple.

[1] https://www.law.cornell.edu/regulations/massachusetts/202-CM...