(a)his turnover during that period on(i)the sales, at the subsequent stages of sales, of such goods as are specified, by a notification, issued under section 6 to be subject to tax at the first point in the series of sales in Sikkim in respect of which tax due under this Act is shown to have been paid to the satisfaction of the prescribed authority;(ii)the sales of goods exempted under section 8;(iii)the transactions not liable to tax under section 9;(iv)the sales of goods which are proved to the satisfaction of the Commissioner to have already been subjected to tax under this Act;(v)the sales to a registered dealer