Clarification/Follow-up by pete4187 on 02/22/05 2:39 am:
I think this is partially correct, although I have heard that amounts under even dollars (99 cents, for example) were used so that cashiers would be forced to make change and be less able to keep some cash for themselves. But why tenths of a cent? Nothing else uses tenths, and 99 cents per gallon would give the same psychological feeling of a bargain as 99 9/10ths, I expect.

Clarification/Follow-up by excon on 02/22/05 2:41 am:

Dude, remember, these are OIL Company execs. There's no figuring out what's going on in their heads. Remember Enron? I don't think they want to change anything.

excon