Nick here from Shopify. Great question, taxes can be difficult to figure out even on the best of days.
This is something Shopify can't answer for you in the sense of, it would be up to your government and where you are located. Once you have confirmed where you should be charging taxes, that's where Shopify would come in and we can guide you on how to set up your taxes accordingly. We can't give tax advice on where and how you should be charging taxes as it is different for every country and even regions within countries. I would advise you to speak to a tax authority or a tax professional if you are unsure about which taxes you need to charge aspect. You can also consult the Shopify tax guides for more information about this. Usually, store owners should only be calculating taxes in places you have a nexus and have registered to collect taxes. From what you mentioned it seems like you have only done that for your own country, and sounds like it's not in the US(if you are talking about VAT)? So my educated guess wouldn't need to worry about touching the US tax settings. But again, this is something I would advise you to confirm with a tax expert.