There's no way to do it completely automatically right now, but you could setup a customer group and a set of discount codes for the same % as the tax that's tied to only be usable by that customer group. Then they'd just need to use the discount code during checkout to nullify the tax charge.
The only other practical way would be making a whole other (password protected) shop for the tax-exempt customers, and setting it up to not charge tax in the first place, but then you're running into extra fees to run two stores.
It is also possible to set up tax exemptions by adding customer tags.
If you have any questions, feel free to reach out to us at email@example.com, we will be happy to help!
Lenka from Sufio Team