One can give money to charity and have it count as a tax write off, but you still can't avoid taxes by threat of imprisonment.
Did not mean subjecting yourself to danger of course. I understand it is very hard for Americans in the US to reduce or avoid taxes. Outside though it is easy and can be done with appropriate accounting and Trust Fund setup in Tax Havens. Just wanted to bring the knowledge that it is permissible in Islam to avoid it and using clever means to reduce taxes paid.
also I am not sure I understand what you mean by this:
whatever reaches nisab (a minimum amount below which you are considered poor and therefore are not required to pay zakat, I think Hanafi methodology scholars calculate it today as US$161 or something)
Nisab نصاب means a minimum value by which if a certain asset class reaches it, it becomes required to pay Zakat on that asset. For the example I mentioned, 87 grams of Gold is the minimum amount you should have before needing to pay zakat for it. So if you have total jewellery of 70 grams, then you don't need to pay zakat off of it. If you have 120 grams of gold in different items of jewellery, then you'll need to pay 3 grams worth in zakat.
What you should do is generally calculate the value of 87 grams of Gold as per today's prices, and that will be your Nisab. Let's say the value of that is 3191 as per today's gold price of 36.68 per gram.
Now you calculate your assets, let's say you have a house worth 250,000, mortgage worth 150,000, savings account with 20,000 in it, and shares worth 30,000. Then your net worth is 150,000, which is clearly above the Nisab level of 3191. So you'll need to give out US$3,750 being 2.5% of what you own. That is of course based on what have been with you for one full year (Lunar year that is, Hijri year of 354 days) then you calculate the value of those assets and subtract Liabilities to have your net balance.
Let's say your house was actually revalued to US$102,000 after the crisis. Then your net worth is actually $2000. Since you have less than the Nisab amount, you should not pay any Zakat.
The part of $161 was about cash at hand, that Hanafi scholars (only hanafi) are calculating based on silver, not gold. Some say if you have more than that amount ($161) then you should pay zakat, instead of having more than ($3191). But mostly this is now a weak opinion, I mentioned to add knowledge that is all.
By the way if that link that I sent was not working properly, use the following one for simple and general calculation:
http://www.central-mosque.com/fiqh/zcalc.htm
This one is a good excel file that is very detailed and you can keep on your computer:
http://www.muttaqun.com/zakatcalc.xls