I just entered my 2nd fueling on Fuelly and am delighted with my mileage so far. However, since my odometer only shows whole numbers, I think the measurements are not as exact as they could be. This seems like an odd limitation for the Prius C's information system. Has anyone found a screen where the odometer displays including tenths of a mile? The owner's manual does not indicate anything.
Remember that pile of paper firestarter you got with the car? the answer is in there. or here in pdf form. 2015 Toyota Prius C Owners Manual and Warranty - Toyota Owners
My trip odometers show tenths. Yours probably do too. But even not using the tenths, odds are that it will average out over time.
Many cars have odometers without tenths. Over the long term, this is totally irrelevant to your MPG computations. Even short term, the small error for lack of a tenth's digit is swamped by the other uncontrolled factors causing daily MPG variability.