Is it ethical to do tax evasion and donate the money?

1. Donations to charity are already tax deductible. No illegal tax evasion should come into the conversation.
2. For the love of God, do not do anything illegal or unethical in the name of EA or reducing suffering. Please.

Thinking that 'the ends justifies the means' (in this case, making more donations justifies tax evasion) is likely to lead to incorrect calculations about the trade-offs involved. It's very easy to justify almost anything with this type of logic, which means we should be very hesitant. 

As another commenter pointed out, tax money isn't 'your' money. Tax evasion (as opposed to 'tax avoidance' - which is legal) is stealing from the government. It would not be ethical to steal from your neighbour in order to donate the money, and likewise it is not ethical to steal from the government to donate money. 

No. Tax money isn't yours.

Edit: fine, I'll add one exception, which is if you don't live in a democracy. The reason is that the amount of taxes in a dictatorship can be determined arbitrarily and isn't tied to any legitimate claims.

I disagree with the other commenters here who say that tax evasion is theft. I think theft requires taking someone else's property, and I don't think the government generally has a strong moral claim to your property.

That said, the penalty for deliberate tax evasion can be severe. You can easily find people convicted for tax evasion who face years of prison and large fines. I believe this downside outweighs the potential benefit of donating your money instead.

Think it depends on where you live, how high your overall tax rate is, and how good or bad your government is. If you lived in 1970s Sweden, had a very high income (Bjorn Borg, Astrid Lindgren) and were facing effective tax rates of 90% +, then some tax evasion might seem quite reasonable, since the state is effectively violating divine law by taking so much. If you live somewhere fantastically corrupt, like modern-day Nigeria, you might very rightly think that the state doesn't deserve your money since it will just waste it in some spectacular way, and you can do more good by spending it yourself as you see fit (even if it's just reinvesting in your own business or whatever).

Mostly, I would say that most of the developed world is neither so corrupt nor has so outrageously high rates as to justify tax evasion, but your mileage may vary.  I do think that some level of tax evasion is perhaps a necessary thing in the world in order to keep governments in check, since almost everyone can evade taxes but only the wealthy can really afford the expensive advice from lawyers and accountants to legally avoid them. The IRS estimates from random audits that something like 15% of federal taxes due are unpaid, largely I think due to how easy it is to underreport your income when filling out your taxes: PAYE systems are quite underdeveloped in the U.S. 

The widespread prevalence of tax evasion might be thought of as a useful check on government power, since it communicates to federal policymakers that excessive increases in federal income taxes will only be met with more evasion. If you want to get all social justicey about it, you might also argue that a little bit of blue-collar tax evasion allows for historically oppressed minorities (Borderers, black people, etc) to build wealth over the generations. At the same time, while a little bit of tax evasion on the side helps keeps the state in check, if everyone did it, things would rapidly break down. But it's a nuanced question and not much more can be said without knowing more about your personal situation. The ends do justify the means some of the time!