When was the 9/10ths added to gas pumps?

Question

When did gas pumps add the 9/10ths

Answer 1

"Exactly when and where the tenth cent pricing practice was first used to set the cost of a gallon of gasoline has been difficult to determine.   Requests for information on this subject addressed to the major oil companies and to the many petroleum marketing associations, with one exception, were not helpful.  A response from the Customer Relations Department of Mobil Oil Corporation suggested that tenth cent pricing probably started no earlier than the late 1920s and early 1930s."