First of all, as a Buddhist you have to follow the national laws and you will never have a problem with them, if you observe Silas correctly. Secondly, the use of tax is not the matter in regard of the later use and so you are not involved directly, which would be different, if you are involved in direct voting for this or that use, or this or that way.
So what to do with it, is a matter of your voting. The act of sharing your part, is just the act of sharing your part and your thought while doing it.
You can tax pretty good as Dana. Important is that you give it without a wish back, for the good of others and the good mind setting before, while and after the act of giving.
And third, if you do not violent taking what is not giving, you even would not have a problem with paying tax. Silas are the way to get free of new bad conscience or bad effects, they are not to use them for your ideas of good and bad (judgment of others) and no excuse for ones disability in letting go. Actually they are a support, because you always need to get deeper into your intentions and ways of thought.
Do not speculate, just observe Silas. And your are not a big patron who shares his own, remember that it is taken and not really yours, so tax is just a way to compensate peoples disability to share.
In countries where gratitude on generosity was naturally practiced, the was long time no need for tax. In times where duties are out and illusory rights are in, quarrels will be not be lessened.
If one does not come in conflict with a higher problem, he does not quarrel with some minor issues. Dig the unwholesome intention up and do not fall into hypocritical ways. Last but not least, if you like to have it easier, there is a reason why people leave their homes into the homeless state. Its good to practice step by step.
And if such thoughts of "I support the bad man" come up, better think on the own greed government of of thought and put a veto if they do not good.