Do you really want rounding?
Normally, for example when using the internal date/time functions, the seconds are stripped.

If you have the number of seconds you can divide them by 86400 to get the internal date/time
Code:
Debug.Print Format(43200/86400,"HH:MM:SS")
Debug.Print Format(43220/86400,"HH:MM:SS")

Debug.Print Format(43200/86400,"HH:MM")
Debug.Print Format(43220/86400,"HH:MM")