It's not hard. It's all arithmetic.
Before people pounce on me for "trivializing it" – I've written, from scratch, Obamacare Insurance calculators that analyzed hundreds of policies with various coverages, coverage tiers, and you could type in things like "If i broke my leg on this policy, how much would it cost?" (all in real-time).
It was a lot of arithmetic but really not that bad (about 150-200 lines of mainly applying coefficients to standard formulas depending on your policy tier), but it was all addition, multiplication, and division. And it really wasn't that bad. Took about 2 weeks.
Update: Just to clarify, an analyst had already done all the legwork of collecting those coefficients and premiums and costs for me. But all I'm saying is that the actual formulas are never that crazy.
I've also written similar calculators for life insurance and travel insurance.
I really doubt the tax calculations are any different.
Ultimately you gotta remember that these laws are made by pretty average humans and have to be enforced by those same average humans. They're going to be vast, but any single rule won't be mathematically complex.