Pre-1965 silver coins, silver eagles, and gold eagles shall be the exclusive medium which the state shall use to make any payments whatsoever to any person or entity, whether private or governmental. Such coins shall be the exclusive medium which the state shall accept from any person or entity as payment of any obligation to the state including, without limitation, the payment of taxes; provided, however, that such coins and other forms of currency may be used in all other transactions within the state upon mutual consent of the parties of any such transaction.