If the value exceeds 5, add the remainder to a new cell. [but not that easy]

Hey all,

As much as the title may make this look like a basic question, it really isn't, so here goes my best description of I have the lucky task of attempting.

Basically I'm using solver to maximize profitability of selling 3 products, but the cost model that we're using has tiers. For the first 5 units sold, we're charging $X, but for the next 5, $X-2, so on and so forth. We're doing that for 3 different products being sold for up to 20 units of each product. I've set all of my constraints, but the only problem I'm having thus far is getting solver to fill up the first 5 before moving to the next 5. Is there any way to format the cell to make it max out at 5 before moving to the next cell and maxing it out at 5 etc etc?

Any help is appreciated. Thanks in advance!

--B

Can you upload excel example with inputs and desired outputs?