Fab data is all in decimal, and handled automatically by machines that work in whatever internal units they need; as far as I know, what you operate in, and export as, makes utterly no difference. Might as well make use of those decimals; rounding them won't even save file size once it's all zipped up!
Holes should be 5-10 mil oversize (finished plated i.d.). More and you need a lot of solder to fill, it fits too loose during insertion, and is probably weaker (easier to pull out, especially for soft leaded solder). There's also danger of shrinkage and cracking or delamination (especially for the pad 'barrel' away from the PCB laminate it's held in, and from connections to internal layers embedded therein) when there's a big blob of solder.
Holes can be as tight as +2 mils, but insertion gets very difficult, and solder doesn't wick well. Most fabs don't do better than 3 or 5 mil tolerance, so you want to be above that, hence 5-10.
I do tend to round hole sizes together, just for neatness really, so as not to clutter the drill drawing. Actually, the fab should be smart enough to do this, and would do a better job rounding to the desired size, based on their available tooling.
For vias, I always use 12 and 20 mil i.d. as standard, with 8 mil as the smallest, reserved for fine pitch or dense circuitry. You can get smaller vias, but they have to be microdrilled or laser drilled, at added expense.
Annular ring is usually 5 mil minimum, 10 preferred. 18/8 is the smallest via I use; larger go up roughly in proportion. 30/12 is enough for small pogo-pins to hit (good for assy/functional test), and 40/20 is good for power connections or soldering test wires into. Pad ODs up to 60 mil or more are good for regular pogo-pins, and can be made as SMT or THT (with any size hole, up to, oh, 40 mil maybe) pads.
My preferred '0.1" pitch header' padstack is 65 mil OD, 40 mil ID, all round, except for pin 1, which is a rounded rectangle pad shape, 10 mil corner radii.
Tim