Using 3 check boxes to determine which formula and result is presented in a cell

[copeterson59]

I am trying to make a data calculation sheet for a boat cell we generally use 2 margins to calculate price but I want to have a custom margins field and check box. As I have it right now check box 1 set is true, checkbox 2 is false and these will generate the margin for 17% or 20% respectively. I want to insert a 3rd check box that is a "custom amount" so when clicked over rides the true/ false from the first two and generates a formula pulling the custom percentage from another cell. Is this possible? first screenshot is the layout the second is how it is set up with the IF formula now. 

[#2]

@copeterson59 

Ideally only one checkbox should be selected and in this case why didn't you insert the 3 Option Buttons linked to the cell A6 so that user can select only on option i.e. either 17% or 20% or Custom. And in this case the linked cell would return either 1 or 2 or 3 depending upon whether you select first or second or third option button and then you may tweak your formula like below...

=B2*CHOOSE(A6,0.17,0.2,B5)

Where B5 would be the cell with custom %. So if user selects the third option Custom, the formula will use the % entered in the cell B5. You may change it to any other cell as per your setup.