The entire reason that tax software is hard is that it can NEVER produce a wrong answer. Plus tax law is about ten thousand times more complicated than you're assuming.

No tax software or expert will never produce a wrong answer, because too many questions have no guaranteed right answer, due to inconsistent interpretatios within the IRS.

Tax filing is a matter of risk balancing, which heuristics are great at optimizing, if they incorporate enough data. Neural networks are ideal for that, but it would take a lot of data gathering to develop the model, from data that isn't easily scraped from Web pages.

People file incorrect tax amounts all the time. It's the government's job to verify the return and either refund you or request more money. There's a decent margin for error, and not all returns are audited so the IRS must also have a margin for error they're building policy and budgets around.

1% of returns filed by tax software have errors, which is infinitely more than 0%

>it can NEVER produce a wrong answer

As the government it should be possible to reduce the negative impact of making mistakes.

>Plus tax law is about ten thousand times more complicated than you're assuming.

Then start simple. You don't have to cover all of tax law at the start.