The Three Methods of Rounding
The USPS defines three methods of rounding: round off, round up, and round down. Let's demonstrate these by rounding 0.105 and 0.104 to two decimal places.
Round off
0.105 rounds off to 0.11
0.104 rounds off to 0.10
Round up
0.105 and 0.104 both rounds up to 0.11
Round down
0.105 and 0.104 both rounds down to 0.10
Which Method to Use?
Normally, you don't have to worry about which rounding method to use when using Postalsoft Presort, Business Edition, or DeskTop Mailer - it knows what to do in accordance to USPS regulations.
If your curious, the round off method is used in most situations. For instance, single-piece weights are rounded off to two or four decimal places, depending on the mail class.
When in doubt, always consult the Quick Service Guide and/or the DMM. You can find both at the Postal Explorer.
