You cannot be taxed for collecting coupons. A coupon is something that can only be spent in one place, just like your SBD. Steem however can be spent in a number of places and can be traded for USD. From my understanding, however, your income isn't taxable until you create a "taxable event". This essentially means converting your crypto to fiat. If it stays as crypto it's untaxable. If you make a purchase or trade, it's the trade that is taxable.
Besides, you are absolutely anonymous when you receive crypto unless it's to a phone owned by a big telecom company, and even then it would be difficult. so the IRS does not know how much you have until you put it on an exchange you signed up to with your ID, you try to convert it to USD fiat which requires an ID, or you try to make a purchase which requires your shipping address.
This article explains it very well.