Adam Clarke on Matthew 22:19

They brought unto him a penny - A denarius: probably the ordinary capitation tax, though the poll tax in the law, Exo 30:13, Exo 30:14, was half a shekel, about twice as much as the denarius. The Roman denarius had the emperor's image with a proper legend stamped on one side of it. It was not therefore the sacred shekel which was to be paid for the repairs of the temple which was now demanded, but the regular tribute required by the Roman government.