"just as no one is morally required to answer a robber truthfully when he asks if there are any valuables in one’s house, so no one can be morally required to answer truthfully similar questions asked by the State, e.g., when filling out income tax returns." Murray Rothbard

Remember, with bitcoin you are volunteering any tax payment you make. That's their only way to get tax from you. You have to voluntarily give it to them. Do whatever makes you feel comfortable, of course.