Indeed, the Merchant Category Classification is the important part.

To further illuminate the OP, 5x has to match specific MCC, which are set as part of the card processing setup for the merchant. There's certainly a lot of consternation about MCC matching bonus earning on credit cards (like this entire thread).

I don't think there's a definitive list, but TPG compiled a list a couple years ago: 4813, 4814, 4815, 4816, 4899, 5943. There's probably more debate about what codes as telecom (T-Mobile stores don't) or what codes as video/music streaming (Playstation Vue doesn't, :/).

Perhaps there should be a sticky for something like this?