What can I do in this situation related to consumer product pricing?

The convenience stores on my campus routinely get their product prices wrong. That is, the product will be marked as one price, but I will be charged another (most of the time they overcharge me). For example, today I bought a bag of Cracker Jacks. On the bag, it says that they cost $0.99 However, it rang up as $1.09.

First of all, is it legal for a store to charge more for something if the price is specified on the product itself? (It didn’t say the MSRP was $0.99, the bag just listed the price as $0.99)

Secondly, isn’t there a state law that says that if a product is advertised at a price, it must be sold at that price? I’m in Maryland.

I realize that the price difference is miniscule, but as a consumer, the principle bugs me. What kind of action should I take, or at least threaten to take?