There is, as you suspect, a carveout:

https://malegislature.gov/Laws/GeneralLaws/PartI/TitleXV/Cha...

(i) ...if there is a discrepancy between the advertised price, the sticker price, the scanner price or the display price and the checkout price on any grocery item, a food store or a food department shall charge a consumer the lowest price. If the checkout price or scanner price is not the lowest price or does not reflect any qualifying discount, the seller: (i) shall not charge the consumer for 1 unit of the grocery item, if the lowest price is $10 or less; (ii) shall charge the consumer the lowest price less $10 for 1 unit of the grocery item, if the lowest price is more than $10; and (iii) shall charge the consumer the lowest price for any additional units of the grocery item. For the purposes of this subsection and unless the deputy director determines otherwise, individual items that differ only by color, flavor or scent shall be counted as the same item if they are identical in all other aspects, including price, brand, and may only vary in random weight. This subsection shall not apply if: (1) there is evidence of willful tampering; or (2) the discrepancy is a gross error, in that the lowest price is less than half of the checkout price and the seller, in the previous 30 days, did not intend to sell the grocery item at the lowest price.