It shall be the duty of each vendor of or dealer in goods, wares, and merchandise who has commenced business on or after May first of any year to take out a license from that time until the expiration of the then current license year--to wit, April thirtieth succeeding--for which period he shall pay upon the whole volume gross of business, including cash receipts and merchandise sold on credit, which has been transacted within the first month during which said vendor or dealer has been in business multiplied by the number of months of the license year for which the license shall be issued--to wit, from the date of commencing business to the following first day of May--at the rate of two dollars for each retail vendor of or dealer in goods, wares, and merchandise, and one mill additional on each dollar of the whole volume gross of business transacted during the first month the said vendor or dealer has been in business multiplied by the number of months of the license year for which the license shall be issued, and at the rate of three dollars for each wholesale vendor of or dealer in goods, wares, and merchandise and one-half mill additional on each dollar of the whole volume gross of business transacted within the first month during which said vendor or dealer has been in business multiplied by the number of months of the license year for which the license shall be issued.