A sellers permit, or business license, or whatever it may be called in your locality is basically another way to collect a tax. Yes, if you are business, you need one. If you provide a service or products you need one. If you can fog a mirror you will need one. They want your money. If they catch you doing business without one it will only cost you more.

Best place to check is where you would pay any kind of tax bill in your area. If they are not the right place, they can probably tell yo who to contact. Or, in some cases that you need nothing. But don't accept that you'll need nothing until you have been told that by 2 or 3 different offices. There are still places where the left hand has absolutely no idea what the right is doing.