One point I want to stress, is that there are many forms of legal taxation, which are even acceptable under libertarian philosophies. Any tax that one can personally and legally avoid without undue hardship conforms with libertarian philosophies -- for instance an interstate commerce tax, tariffs, excises, user fees etc. Then, any tax that is apportioned is legal by the Constitution.
The argument against income and property taxes are much deeper than legality and amounts. Income tax assumes that the government owns the individual and their product, and only allows the individual to 'produce' at their permission. Property tax assumes that the government owns all property and only allows the individual to hold property at their permission.
Sales tax is more of a grey area, libertarian-wise. Something like gasoline tax paying for roads, a(n albeit weak) case can be made that "commerce" is a line of communication upon which the government has authority, due to the use of Treasury notes to affect said commerce. This assumes that the government has a stake of ownership in all commercial transaction, (which is why it's grey) but a valid argument can be made that a federal government DOES have a stake in the general notion of 'commercial transaction' simply because there is a "gross domestic product" supported by the US Treasury system. The use of Treasury notes in order to produce commercial transactions, is what gives legal claim to a stake here, and can be avoided by barter outside of US Treasury notes. Also, sales tax can be avoided, and the government can be de-funded, simply by the people choosing not to buy things commercially (ie - barter).
If stuck with a sales tax, my "perfect world" would be to employ something somewhat radical -- tax not sales themselves, but the use of treasury notes specifically. Of curse, this would require a radical change in the US Treasury department. First of all, money would have to be taken out of the Federal Reserve and returned to the US Treasury. Somehow, tax would have to be distinguished between coinage, paper, and electronic transactions. All of this of course, would be a bloody nightmare to even attempt to implement; but would permit an "opt-out" system without restricting commerce. If, for instance, coinage were based on precious metal value and taxed at zero percent of transaction, electronic transactions were based on precious metal holdings and taxed at 7%, and paper money (based on precious metal certification holdings) taxed at 14%, for instance. The more heavily you rely on the governments "services" the higher the tax you pay. I'm not saying that's a 'good' system (I just invented it on the fly as I typed) but it would be a 'sales tax' that managed to dovetail with libertarian principles...especially if the coinage based on precious metals minted coins that reached as high as $100 for instance. Thus people could choose to use all coins, or all paper. Paper would be easier to trade in, but it puts a higher burden on the Treasury.
buh- buy 
