Package shipping weight 15.3oz. - How do I buy 1st Class Package Shipping Label?

[jbuckeye27]

When purchasing the shipping label after an item sold I want to select First Class Package. 

The details for USPS FIRST-CLASS PACKAGE list the Max Weight is 15.9oz. If a package weighs 15.3oz, how do I enter the correct weight to purchase 1st Class package?   I called ebay and the person said just enter 15oz, even if the package is up to 15.9oz.  Is this correct?   I am worried that the package will be kicked back for insufficient postage.

Thank you for your input and suggestions!!

[disneyshopper]

Just enter 15 if unable to enter 15.99 .

[jbuckeye27]

Thank you!