Upon the filing of an original schedule of prices and after the effective date of any schedule of amendatory prices, all prices therein stated shall be strictly adhered to by the filing licensee, and any departure or variance therefrom by a licensee is a misdemeanor, except that the transfer of beer between wholesalers who sell the same brand in package is permitted without filing the schedule of selling prices. Each sale or transaction involving a violation of posted prices under this chapter is but a single offense or violation of this chapter regardless of the number of articles covered by the sale or transaction.