Bob,
I appreciate that you are thinking of rounding to thousandths of a day. Actually, by rounding to tenths, over the course of a year, you end up short about 2/3 of a workday (5 hours). You might be surprised how cranky an employee can become if they are missing their 5 hours. Rounding to a thousandths of a DAY will leave you about 1/2 an hour short per year, which isn't bad.
Where I work, our H/R accumulates leave by the 1,000th of a HOUR (3 decimal places) then rounds to the hundredth of a hour for display, which is typical. That leaves you OVER about 3 minutes A YEAR-pretty accurate! Yes, you can handle shortages administratively - but HEY! - if technology can do it for you, why do it administratively.
Thanks again for all your work on this project.