Any conveyance used as a means of transport for carriage of taxable goods without the cover of documents as may be prescribed in this behalf shall be liable to confiscation, unless the owner of the conveyance proves that it was so used without the knowledge or connivance of the owner himself, his agent, if any, and the person in charge of the conveyance:

Provided that where any such conveyance is used for the carriage of the goods or passengers for hire, the owner of the conveyance shall be given an option to pay in lieu of the confiscation of the conveyance a fine equal to the tax payable on the goods being transported thereon.