For example:
Item 1 ----------- 1$
Item 2 ----------- 1$
Item 3 ------------ 0.5$
After the description of Item 1, you can see:
Item 1 + Item 2 — 1.5$
Item 1 + Item 2 + Item 3 — 2.25$
And so on…
I would love this as well.
But by category groups and the option of % off.