Custom User Roles for Custom Post Types

How would I create custom user roles for custom post types? I am creating a somewhat specialized multisite setup where from the outside looking in, it will look like a single site. However on the back end, would be multisite with sub-directories.

On one of the subsites, I created a custom post type for jobs (for HR) and want to create a custom user role so that if they have an assistant that *just* needs access to post jobs and nothing else, we can limit it to just that.

How would I do that?