Eskimospy is correct.
Roberts wrote the penalty was a tax for Constitutional purposes, but not a tax for the anti-injunction law. That's counter-intuitive at first blush. Will need to read the part of the opinion that addresses this.
Fern
I've just finished glancing through Roberts' opinion, and it is quite dubious to be frank. ()

What you're saying is what he is indeed saying, and he isn't making a whole lot of sense with that. It must be tough to be Roberts, who wants to be remembered a great chief justice in the history of the U.S. Supreme Court.
However, as for the outcome and the lasting impact, a true conservative/libertarian should breathe a sigh of relief. Liberals worried that conservative justices would swing their magic wand to strike down "just this one law," a la Bush v. Gore for political reasons. Instead, what he wrote is the opposite. His opinion actually attemps to shrink the federal government in the future, while letting "this one law" survive. It is political, and it won't benefit the liberals in the future. I am now about to read Ginsberg's concurrence/dissent, and I suppose she isn't happy with the chief's reasoning.
So if you are truly concerned about federal government's overreach or some other Orwellian scenarios, then you can be assured that this decision will not be a spring of slippery snakes (or slopes). However, as I suspect, if what some of you really wanted was not a health care reform, a limited government, individual liberty, but a political defeat of Obama - then congratulations, you are defeated.
Edit: He also actively provokes people to "vote" if you don't like a certain law. ("I'm not responsible for your stupid president")