Remember: your digital tokens are not taxable until you redeem them for U.S. dollars. If you leave them in a wallet or exchange somewhere, they are simply considered so much "digital air." Upon conversion to FIAT, taxes matter.

This is not correct. Any crypto-to-crypto exchange is a taxable event under US law.

Additionally, mining results and airdrop (which STEEM would qualify for) are taxed as ordinary income at the US dollar value upon receipt. So when you claim your post rewards of 3 SBD + 1 SP, that's taxable income at the USD value of those quantities on that date.