My shipping policy states 100% amount listed for first most expensive item, then 50% of the amount listed for all other additional items.  I 

Most groups are shown as a group then I zoom in item by item.  total scv is shown from a recent catalog on most items.  Many of my discount postage lots are collectable and will sell over face.  this is not discount postage.  All items on my page are relisted till sold with a very often price reduction if appropriate.