IANAL, or an accountant, etc, but if I’ve learned anything from ravenously consuming Trump family news the past few years, it’s that ignorance of the law actually is a defense in cases around taxes, and the IRS has to satisfy a standard of proving bad intent in order to really screw you.
Again, IANAL, do your taxes, please. But it does seem like the system is legitimately designed with an ethos of just making sure taxes get collected and isn’t about being vindictive.
Having dealt with tax authorities in several countries, it's a recurring theme that they have no interest in coming down on you hard if you seem to be trying to do the right thing and make actual efforts at compliance, as they have their hands full putting actual effort into dealing with people actually trying to evade tax.
What I always do if in doubt is to attach a letter setting out my assumptions. I've outright had to tell the tax authorities I didn't know the real numbers one year, because I realised shortly before filing that I'd lost documentation in a move, and so a whole bunch of details were estimates. Even that was accepted without additional documentation.
Of course I'm sure there are countries that are worse.
There is no way that would work with the IRS. Anything you estimated and can't provide documentation for will automatically be considered void and non-existent by the IRS if that thing reduces your tax bill.
If you think you have about $5k in valid deductions, but you can't provide any documentation upon an audit, then that $5k will be reduced to exactly $0 and you will owe all additional taxes plus interest and penalties.
Again, IANAL, do your taxes, please. But it does seem like the system is legitimately designed with an ethos of just making sure taxes get collected and isn’t about being vindictive.