The monthly sewer service charges as established in this chapter shall be rounded to the nearest five cents and shall be rounded downward if the calculated figure lies equally between adjusted rates; provided, however, the minimum equivalent residential unit charge shall apply for any month or portion thereof that service is rendered and the minimum charge shall not be prorated on the basis of a partial month’s service. (Ord. 448 §1, 1977; Ord. 166 §10(E), 1970).