Legal Question in Constitutional Law in Texas

No. That would be true even if the ACA did exceed the government's authority -- which the Supreme Court has already said it doesn't.

"Pleading the fifth" refers to refusing to testify on the grounds that the testimony might incriminate you (no person "shall be compelled in any criminal case to be a witness against himself"). Abuse of government authority is not a basis for pleading the fifth. As Mr. Hoffman notes, the Supreme Court has pretty much said that the ACA is within the authority of the government (we, the people) to enact. But if you actually prosecuted for cheating on your tax return, then yes, you could refuse to testify against yourself, though you could still be convicted without your testimony.

The ACA is certainly troublesome in that it continues to give insurance companies a wholly unnecessary "take" out of the cost of health care, but so long as the corporate interests behind profiting from human illness and accidents (or fear of the economic consequences of illness or accident) continue to have political influence in Washington, we are not likely to have a "single payer" system in which you no longer need health "insurance" because you already are assured of health care. The best that the current political system has allowed is the ACA. As much as you may prefer to cut for profit insurance companies out of any role between you and your doctor, too many members of Congress are beholden to the health insurance lobby.

Rather than looking to the Fifth Amendment of the U.S. Constitution, you might want to consider ways that your local or Arizona government could begin lessening corporate influence over human life, and advocate for health care without health "insurance".