The resolution for sleep is not guaranteed in any manner by POSIX. In fact, on certain (crappy) systems, it may even change during the running of a program due to process load (by yet again undefinable amounts). sleep is most always (if NOT always) implemented using alarm(1), so your problem stems back to that function. sleep should be used for coarse wait control- hence, it is only useful for "user-level" time manipulation. A user can't determine the difference between a second and a second +1/6 second.

For lingering on a socket, you can use the SO_LINGER socket option if that's available to you, or you can continue to use your method with a bogus select where POSIX guarantees a certain time resolution due to constraints on the timeval structure. Sun seems to follow POSIX (to a certain extent), so that would work better for you in this case. Good luck!

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