pjw0: So it looks like now you can enter a ZIP code for tax that looks up municipality names, but there's no save button or indication that it's saving (unlike the spinning icon that appears when you change language or country).
It doesn't change anything when trying to complete an order from your cart, and it gets cleared out when you clear your cookies.
Progress!
I just tried ordering a game and it did take into account the location I put on my account and charged the correct sales tax. So the new system seems to be working now for anyone, like me, who was waiting for a resolution to the sales tax issues.