I have a requirement to hide or show tabs on an application based on user role.

Hello, so in order to do this you need to edit the "Page Sharing" settings for the page defining the navigation item (i.e. the tab). Open the page in the designer portal and select the "Actions" dropdown from the upper right corner. There should be an option here called "Page sharing". From here you can restrict who can see the page by adding/removing specific users or groups.

In order to restrict by group use: 

a!isUserMemberOfGroup(loggedInUser(), cons!CONST_SECURITY_GROUP_POINTER)

You will need to use a constant that points to your security group. You can create the constant in editor by clicking on the constant icon