I know it's not required by law to scan it, but it might be a store policy, in which case I don't think there's a law disallowing that kind of store policy. They'll tell you to shop elsewhere, and every big store does it.

The only law involved is the one that penalizes them harshly if anyone underage manages to buy liquor. If fake IDs are less likely to pass that scan, maybe that's why they do it.