Just spoke with someone on chat (very good experience, by the way) and this is still not possible. The whole point of providing the ability to capture taxes separately is to make my job easier when filing with my state's taxation department. If I have to figure out which items were incorrectly priced due to non-taxability, I've lost that convenience and I might as well *not* separate taxes from my product prices.
Please, developers, add this feature. Wix + Weebly handles this properly! A simple checkbox on each product would suffice.
I have to admit that I'm amazed this site/product/store is as popular as it is without this feature - it really made me think I was missing something. But nope.
I hope this gets resolved so I can switch to SquareSpace from a competitor - I like the looks!
