I am my company's administrator and I would love to grant permission to a user to be able to access the Performance Center, but I cannot find any such permission in the existing Roles or in any of the options for a custom role.  I have not found it in any of the documentation nor have I been able to get anyone to tell me how to do this.  

Keep in mind that this user only needs access to the things that are in the Performance Center (reports and graphs).  The user currently has the "View company reports" role which gives access to Reports.  This also includes a link on the page to the "Performance center".  This lands the user on a page which contains only the graphs BUT there is no link to get back to the reports.  It is an awkward one way trip.  It looks to me like the developers had the right idea at one point and then it got broken.