First, I just want to echo everyone else's sentiments that you shouldn't worry about it at all.
Secondly, to perhaps ease your thoughts of feeling like you've been cheated here (since I'm pretty sure they round correctly), is it possible that your 3.645 is actually something like a 3.6449 and therefore, looks like 3.645 when rounded to the thousandths, but is correctly a 3.64 when rounded to the hundredths?