We have a marvelous thing in developed countries where the IRS (equivalent) already knows how much your tax should be paying[0] and you basically have to just look at a few numbers and click "That seems right". They even have a form where you can change things that aren't correct! Marvelous, I know... we've had that for 15+ years in Denmark.

EDIT: To add, if you get it slightly wrong... you're fine, it'll be adjusted for in next year's taxes.

[0] ...because it has to, in order to investigate evasion.