I agree it is not a tax. If not a tax, then Congress has no constitutional granted right to penalize American to buy some products that some American choose not to. Then the entire act should be unconstitutional and must be thrown out.
What Justice Robert did is giving an excuse that is denied by Obama to upheld the act.
Justice Robert wants to keep the act and throw it back at American people by claiming it is a tax so do what you want to do with it, pay or not pay, your choice.