(a) that no tax under this Act shall be payable by any dealer having his place of business in the State in respect of the sales by him, in the course of inter- State trade or commerce, from any such place of business of any such goods or classes of goods as may be specified in the notification, or that the tax on such sales shall be calculated at such lower rates than those specified in sub- section (1) or sub- section (2) as may be mentioned in the notification;