I'd just give a call and ask if this is going to be a consideration for you. Unless it is a service dog you'd have to ask.
Mast General Store is NOT dog friendly in terms of dogs walking throughout the store. However, there is a waiting area in front where husbands and others who don't want to shop can sit in comfortable chairs. Dogs on a leash and not roaming around might be okay in this area.
Get quick answers from Mast General Store staff and past visitors.