Getting divide by zero errors from ms-usps.php

One of my users is getting some nasty looking errors on the front end during the checkout process, just after shipping setup.

She is using the USPS shipping module, and after a customer enters their information and selects the USPS shipping option and clicks "Continue Checkout" the confirmation page loads and at the top these errors are displayed:

Warning: Division by zero in /home/teatrade/public_html/wp-content/plugins/marketpress/marketpress-includes/plugins-shipping/mp-usps.php on line 896

Warning: Division by zero in /home/teatrade/public_html/wp-content/plugins/marketpress/marketpress-includes/plugins-shipping/mp-usps.php on line 896

Warning: Division by zero in /home/teatrade/public_html/wp-content/plugins/marketpress/marketpress-includes/plugins-shipping/mp-usps.php on line 896

Not sure when it began, but it was reported by a customer who was trying to make a purchase. You can replicate it on the live site: http://us.the-devotea.com

It doesn't seem to actually break the checkout process and the customer can continue on to payment, but the errors look pretty scary.

Has this been reported by anyone else yet? Do you have any idea what is going here?