Here's the scenario:
1. Buy BTC and ETH on CB with USD, hold them.
2. Months later, buy BTC/ETH, transfer to another exchange (Bittrex/Binance) and immediately buy an altcoin and hold.
So (1) isn't a taxable event because I never sold them (unless I'm forced to use FIFO reporting, then it gets murky - but my lots are very clear/specific).
(2) apparently is taxable, but since I did the entire transaction within an hour, do I still need to report it? The gain/loss would be tiny since the entire lot transaction was done within an hour (usually less).
You are completely right that (1) isn´t a taxable event.
(2) is a taxable event even if the gain/loss is tiny. However, this isn´t really a problem,
because due to the small size of the gain/loss there is not really an incentive for you to not report it.
E.g. if you make a gain of 40 $ during the transaction time you can simply report it, because a small
amount isn´t going to increase your tax bill in most cases.
I´m not a US resident therefore take my advice with a grain of salt. However, I have been
reading a lot about the subject of taxes in various countries and am pretty sure that
the advice above is correct.