We've just come across a strange issue in CartThrob (v2.3.5; EE 2.5.5) where the tax is calculating, but only somewhat.
We've got several different tax rates setup for two states: NY and CA. When using a NY zip code, the tax calculates correctly every time. For CA though, it always uses the first tax rate listed and ignores the others, regardless of zip code.
Here's a screenshot of that part of CartThrob: http://cl.ly/RpCc
With that set up, if I use 93657, whose tax rate is 8.975, it still gets calculated as 10% (the first CA tax rate). If I move the first listed CA tax rate of 10% to the bottom, and try to use 93657 again, it then defaults to 9.5% (the new first listed CA tax rate).
I have no idea what could be causing this issue. Any ideas?