The following rules apply to the posting of prices of retail sales of motor fuels. As used herein, motor fuel means any fuel used in motor vehicles including, but not limited to, gasoline, diesel, propane, and alcohol-gasoline blends. As used herein, motor vehicles shall include all wheeled motorized vehicles, and all boats and airplanes.

(1) The posted or advertised price of motor fuel at retail outlets must be available to all consumers. Any condition or qualification required to obtain the posted price must be clearly displayed in letters of contrasting color at least one-third the size of the posted price and immediately adjacent thereto.

(2) The posted or advertised grade of fuel must be clearly displayed in letters of contrasting color at least one-sixth the size of the posted price and immediately adjacent thereto.

(3) A cash price may be posted or advertised if the posting of the price clearly shows it to be limited to cash purchases. The information shall be in letters at least one-third the size of the posted price and immediately adjacent thereto.

(4) If mixed case letters are used to display the grade of the fuel and any condition or qualification, the size requirements of the letters apply to the upper case letters and any lower case letters must be in proportionate scale.

(5) Cash and credit sales. If a retailer elects to establish separate islands or individual dispensers for cash and credit sales, the islands or dispensers shall be clearly marked as such in letters at least six inches in height and of proportional width.

(6) Posted prices of motor fuels at retail outlets shall include all federal, state, and local taxes.