In order to cash out a check, a new department needs to be created. Start by going to Store Management and then Department.
FInd the + New Department Button on the top right.
In the new menu that appears write the name as Check Cashing and then set the correct flags. The Min and Max will be used to dictate the lowest and the highest possible amount allowed for a cashing in a check.
Be sure to select save changes to save the department.