The main thing that's a pain (extrapolating from stock) is if you buy and sell a lot. The tax is on the gain, but which one did you sell -- you need to keep track of each price you bought (and how many) and offset the amounts against sells.
I think you are allowed to average, but this might not be beneficial with big swings.
I think you are allowed to average, but this might not be beneficial with big swings.