As regular shippers know, the post office has an exception to the "rounding up" rule when it comes to postal rates. To avoid having a huge jump from 15 ounces (first class package) to 1 pound (priority mail), the post office created a 15.9-ounce rate that keeps a small parcel in the first class mail rate.

I discovered this morning that although Ebay will allow sellers to put 15.9 ounces as the weight in a sales listing, they will automatically charge the priority mail rate for anything that is more than 15.0 ounces. Moreover, when shipping that parcel, they will not allow "15.9" to be entered in the mailing process because they don't allow decimals - it will come out at 159 ounces, or 9 pounds 15 ounces.

If you are planning to list something that will be between 15 and 15.9 ounces, you might want to avoid surprising the buyer by charging the full 1-pound rate.

Paypal shipping also will not allow the use of decimals and will treat 15.9 ounces as a pound, triggering the much higher priority mail rate.

Stamps.com, on the other hand, still allows the 15.9-ounce rate.