The cryptos are largely denominated in Bitcoins, since it takes bitcoins to buy them. If you trade a stock in USD in your Fidelity account for instance, and you get back in after selling it, then your cost basis is adjusted so that it is considered as never being out of the position. I don't see why cryptos would be any different. The taxable event should work like this. Invest dollars into BTC, buy other cryptos still in BTC. When you sell your position in BTC to turn it back into dollars, bam, pay your taxes...

Thank you for sharing...