I've just noticed that there's a bug with the chekout js.
I've set up a site (http://store.mixis.com/) that has different tax rules for different provinces in Canada. GST for most provinces, GST + PST for Ontario, and HST for Newfoundland, New Brunswick and Nova Scotia. The problem appears after, you choose one province, and it automatically adds the correct tax(es) for that provinces. If you then switch your province to another province, that first provinces taxes are still present in the tally, along with the new provinces taxes.

My first instinct would be to go into the js and force the tally to remove previous taxes when part of the form, that effects tax rules (state / province selector) gets changed, and then add the tax for the new selection. But ... I am not so saavy with this framework. So far I haven't had the need or desire to tinker w the js - I've just been content to appreciate how clever it is.

I'm sure that this is a bug that must be affecting other sites too.