I misfiled stuff a few times and got fined, it's annoying but it's not something that will break your bank.
The behaviour of the tax office varies quite a lot from country to country tho.
But don't trust me, ask your lawyer.
New Zealand. The Accident Compensation Corporation, a compulsory insurance scheme, is absolutely feral. Will crush you "because rules" without a thought.
Each time I got a piece of mail asking my to call the IRS to clear it up, and every time the agent was nice and very helpful clearing it up, and not fined.