We don't deal with that case adequately right now. It's up to chance which one you get charged. For customers (ie. one-time sales), we unfortunately lump this i

We don't deal with that case adequately right now. It's up to chance which one you get charged. For customers (ie. one-time sales), we unfortunately lump this into "get it close enough and the taxation bodies won't really care". For merchants located in these two-rate zips, we can usually work around it, targeting the correct rate with some ugly hacks. This is something I'd like us to do better on. I have an idea for how to improve without adding an intolerable amount of complexity or expense, but I haven't had a chance to implement it yet.