"Kiran is saying that the function does always sleep for the MINIMUM number of milliseconds specified."

I'm not sure what you mean. Isn't that exactly what it says it should be doing on MSDN? Can you rephrase that?

Also, it is not a function which sleeps. It is a method to tell the OS not to execute the thread for a number of ms.
So Sleep() is only a message that you send to the OS. The OS is an asynchronous, time discrete system and you are sending a message to it at an arbitrary moment with a request for a delay near its granularity. Should one expect large percentual errors, or should one sit back and think: "I think it'll work just fine, and if it doesn't, let's blame Windows"?