To make CheckBox Mandatory

I have a checkbox having ID as "finalCheckout". It is optional checkbox for user to select. If it not selected then it's mandatory to select atleast one checbox that is in another DIV container having ID as "mainDiv". ("mainDiv" is the ID of DIV container").

If the checkbox having ID as "finalCheckout" is checked then it's not mandatory to select any checbox that is in next DIV Container having ID as "mainDiv".

Hope you will be understand what I want to implement. Currently outside office so unable to post actual code what I have done. Can please anyone assist how we can implement it using Jquery.