Albert Barnes on Matthew 22:19

The tribute money. The money in which the tribute was paid. This was a Roman coin. The tribute for the temple-service was paid in the Jewish shekel; that for the Roman government in foreign coin. Their having that coin about them, and using it, was proof that they themselves held it lawful to pay the tribute; and their pretensions, therefore, were mere hypocrisy.

A penny. A Roman denarius, worth about 14 cents, [sevenpence halfpenny.]

(1) "penny" or, "In value, sevenpence halfpenny