I am thinking to start I will run all sales through Etsy, so the $value will be included in my taxes, as well as state taxes when applicable. For now, if people want to pay with steem, then they can simply pay me (I don't have enough steem for it to matter much. I will ask customers to use the Etsy order number as the memo, so if I were to be audited I could show and match sales to memos.
However, if more and more people start paying with steem, I would open a second steemit profile, just for shop stuff. Only creating posts that show new items, and having all payments go through that wallet. This way I can accurately account shop stuff vs personal.
HOW the taxes are calculated in Steem is another matter entirely. That part I don't know, but @lexiconical and @rok-sivante have been talking about it here
https://steemit.com/taxes/@lexiconical/valuing-steem-rewards-as-taxable-income-is-a-vast-overstatement-of-tax-liability-part-1