I think your best options is just to use a Custom format for the Elapsed value (Which is a TimeSpan) like this:
Private Sub Timer1_Tick(sender As System.Object, e As System.EventArgs) Handles Timer1.Tick
Label1.Text = stopwatch1.Elapsed.ToString("dd\.hh\:mm\:ss\.fff")
End Sub
where fff
is the optional number of milliseconds you require - just specify more or less f
's as you want.
Note that this won't round the value but in the case of a stopwatch you wouldn't actually want to round it anyway.