Application for renewal of a license shall be made during the license renewal period in the current license year in order to renew a license for the next following license year. The license renewal period shall begin on January 1 and end May 1 preceding the license year for which renewal is requested. A penalty of 50 percent of the basic license fee shall be assessed in all cases where the renewal fees are not paid on or before May 1, preceding the license year for which renewal is requested. This section shall not apply to retail sales licenses.