There would be machines which produce energy in any form where source is future.
Essentially infinite energy solution. So humans would essentially have infinite energy but if you are allowed to go anywhere in time then why would you stay i ln present. You would immigrate (for lack of better word) to a time when is most suitable and to your liking. You would die in 80 years why do you want to spend time in current world time if you can do better.
It would become like a multiple reality world where like minded people would come together in same reality and people who disagree with them go to their own echo chambers. I belive most people would be looking for fundamental human desires like food, comfort and sex so people will go to time where they get it most easily.
The tax is on the value , if you declare your washing machine has value of 1$ then the tax would be labelled accordingly but that would be a fraud.
Hence if you order parts of the washing machines you would have to declare value of the individual part and it would be taxed accordingly.