When the US Gov uses an IMPAC card to buy a $15 dollar hammer from anyone, it costs $15. Period. The vendor processes the IMPAC card the same as it would any other Visa.
The ignorance of many is coming through on this. TankerKC you are exactly correct - the IMPAC card looks just like any other VISA and is processed exactly the same. If Home Despot is not going to take that VISA than why should they take mine? They won't because as a Vietnam Veteran I will go to Lowes or better yet take my business to a locally owned "mom and pop" store.