I always interpreted that tax passage as Jesus saying that we should return all our money to caesar, i suppose if we trusted/cared for each other enough and tried to help one another according to our individual strengths, then currency would no longer be needed and caesar would end up with a huge pile of coins that do indeed belong to him but have been rendered worthless, render unto caesar what belongs to him, and to god what is his.
Maybe Jesus was talking about how the importance of taxes disappears when we begin to serve one another, and by extension rendering to god what belongs to him at the same time, by following his law.