I'll add that I tired it another way with just one entry and it appears to have worked.

Since I needed my end result to be a negative number/credit.  (I was going from $12.50 to $7.95 resulting in a $4.55 credit.)  I did  credit memo.  I put in 100 items for $12.50.  I went down a line and put in the same inventory item only this time I put in a -100 items for $7.95.  This resulted in my total for the credit memo being $4.55.  And my inventory items being zero.  Now I just have to finish my credit memo steps and to step 2 of the bank deposit and then step 3 of pay bill.

This can also be done in the reverse/opposite with an expense.  If I needed to have my inventory item cost more I would make an expense.  I would put in a -100 at $7.95 and then on the next line I would put in +100 at $12.50.  This would leave me with +$4.55 at the bottom of the page.

I played around with things and I think all of these things solve my problem.