There is no comparison. The merchant can refuse to sell to you, but doesn't claim the right to actively harm you. If you ask for help and the merchant refuses, you are no worse off than you were before. The government, on the other hand, does claim the right to harm you; taxes are but one example. The government can and does leave you worse off, whether you want to interact with it or not.
Back on-topic, the effect of the IRS's demand for USD is similar to the effect of a merchant's demand, with two glaring exceptions. First, the IRS is far larger than any mere merchant, and thus has a proportionally greater effect. Second, you can't choose not to "do business" with the IRS. If any other merchant insisted on USD you would have the option of shopping elsewhere, or going without. Not so with the IRS.
Look at the bigger picture here. We live under this government, the government renders services for us, and then charges us with a bill. If we do not pay the bill, it comes after us. If you live in an apartment or a resort, the business renders services for you, and charges you with a bill. If you do not pay the bill, they can come after you. True, we have a government to protect us from the business coming after us with guns or throwing us in private prison, but the overall set-up is practically the same. Even down to the point where if you don't want to do business with the resort, you can choose not to. Don't want to do business with the IRS? Don't live on their "property." (Personally, my family has refused to "do business" with the Soviet Union) From a "giving the USD value" point, they really do seem to work the same: provide a service, serve you with a bill, collect whatever currency they can themselves use. And I guess just like any other business, they wouldn't care what $1USD was worth, or how much of it you needed to pay for a basket of goods, as long as the value was stable, and had SOME value.