Just went through this for a clients e-commerce site and wanted to share the solution I was directed to in case anyone was unaware of the updates. Squarespace now partners with TaxJar which automatically calculates your taxes for you and you get to have a free account on TaxJar if you join it through your Squarespace.
We set her state to Massachusetts as she also has a store front there. This automatically calculates all taxes for us based upon MA rules. Then within Squarespace, if you go to each product under organization you can assign a tax category to items that may need to be taxed differently in your state... for us this was clothing which needs to be 0%. So all her clothing will have this tax category selected so that these items are not taxed, and all other products I leave it blank so they are taxed at the 6.25% rate. More on it here under Step 3.
