It is appearing as though LFS rounds any fractions down, instead of rounding fractions above .05 up. A number of racers in our league got caught out tonight, 36 laps at supposedly 1.1%= 39.6. 42% was still about 0.8 short, so fuel consumption appears to have been more like 1.18ish, which should show as 1.2. Obviously it's easy to allow for once you know - it's just not intuitive. I don't feel this is a major flaw, I don't expect it to be worked on instantly, I post it to assist with the development of an intuitive UI.

Well, probably no rounding, but just a decimal cutoff altogether. I agree though, it should always be rounded up to prevent such situations as described by you.
Personally, for fuel calculation I always add 0.1 to the shown percentage itself, instead of calculating from the shown value and adding an arbitrary amount on top after doing so.

Quote from AndroidXP :

Well, probably no rounding, but just a decimal cutoff altogether. I agree though, it should always be rounded up to prevent such situations as described by you.
Personally, for fuel calculation I always add 0.1 to the shown percentage itself, instead of calculating from the shown value and adding an arbitrary amount on top after doing so.

Both good points. I'd already decided to do the 2nd