In New Zealand, income from a job where you are an employee (most people) is handled by a system called PAYE (pay as you earn). It's automatically deducted from your pay.
Bank account interest is handled by RWT (residents witholding tax), automatically deducted from your interest. If you're not in the top tax bracket you need to tell your bank, or they will overtax you.
Every year you can, if you wish, ask for a "personal tax summary" which states income and tax. If you paid too much tax, e.g. if you took unpaid leave, said overpayment will automatically be refunded. If your RWT rate was wrong you can ask for a refund of that, too.
If you made donations you send in a form (1 page) with receipts, and get a refund.
If you're a small business/self employed/etc then yes, you have to work out how much tax you are supposed to pay. But most people aren't in that situation.
Isn't that what IT people do? Optimise for the common case?