This question was originally asking for a list of all merchants considered grocery stores in the US. The accepted answer (mine) talks about how merchant category codes work and suggests a way to determine whether or not a store is categorized as a grocery store.
The question was closed as "seeking product or service recommendations."
The question has since been edited so that instead of asking for a list, it asks how to determine whether or not a store is considered a grocery store. It's a good question that has recently been asked again. In my opinion, it should be reopened.