Handling fees, along with UPS/USPS fees, on a "per item" basis?

[Ajeh]

Oh wait I vaguely remember you from a while back ...

Are you still doing this?

What we want is to charge the appropriate UPS/USPS shipping fee, then add a Handling fee of $3.00 for 5 items or less, $6.00 for 6-10 items, $10.00 for 11-20 items, etc.
The items are all the same weight and ship in custom boxes/packages that the client has (one box per item).