For cases where there are decimal points ..... having leading zeroes to the left of the whole number (integer) part can be a distraction, or even confusing. And for those that reckon they don't know when the roll-over occurs..... then just put a marker on the front face, or some instructions that tells the user how many significant digits there are all-up in the display.
Somebody also mentioned that leading zeros can indicate when roll-over occurs. But normally, roll-over for an odometer is probably not even on somebody's mind when driving.
But if somebody wants leading zeros for their display ..... then that's ok too, as that's the way they want it.
I think that you should actually try using fixed-point math, do the work.
"For cases where there are decimal points" --- right over your head.
The machines I made tapes for used 5 digits. From high order to low:
10's of inches
1's of inches
Tenths of inches
Hundredths of inches
Thousands of inches.
We used 1000's of inches the same way that in electronics we take a milliamps.
The machines I made tapes for back then were 60's up to 1980 tech. Reading the high order values first worked easier with less circuitry. To move an X-Y table to X05 Y0375 may seem counter-intuitive to you but it is not to anyone trained to work in the field and it is downright native to the machine.
"Somebody also mentioned that leading zeros can indicate when roll-over occurs. But normally, roll-over for an odometer is probably not even on somebody's mind when driving."
If I'm looking at buying used car that shows wear and the mileage is too low to be all it has covered, knowing how many digits to rollover tells me something very real.
This is also true of electric, gas and water meters. You see the dials and when the current reading is less than the last reading you know that the meter has rolled over and you require knowing the number of dials to calculate usage.
If your paycheck depended on it, you'd know these things. Mine did, moreso when I wrote software to do these things and more. I'm not joking or philosophizing or trying to figure this out as I go, I covered these things before 1990.