No disagreement at all that ERPs are generally garbage, especially for how much they cost. But this comments makes me think you have never dealt with international taxes. The rules are insanely complex, there is no global standard for communicating the tax, multiple systems have to be in sync with each other, and some systems even use different rounding algorithms...

I'm all for blaming the software (which by the way in this case is made by a huge company I am 100% sure you know and costs hundreds of thousands of dollars to operate)... but the real problem here is the complexities of tax (I used Canada as an example but the US is the absolute worst because each state makes their own lows) is not a software quality problem, it is a data and open standards (or lack their of) problem.

But since the lack of standards is not being fixed any time soon, sometimes it "is" the user's fault.