There is no way to tax it 100% or course. You can get away with not paying taxes by dealing in cash only. This will be possible with bitcoin or any other currency.
But the government can easily figure out which businesses are accepting bitcoin as payment if they want to tax it. A business will have to move between cash and bitcoin to pay expenses like payroll, vendors etc. and that's very hard to hide unless you lie about it (and even then you will got caught if audited).
It doesn't matter if you are using wampum, tree bark or bitcoin. If it becomes a large enough medium of exchange it will be taxed.
How are you going to tax a medium of barter? You can't, for it you try then it's legitimized and the government has put a value on it.