SQL Server Login Properites Box - Do I need to check off master, msdb, tempdb?

On the SQL Server Login Properties box for a user where you select to permit databases, I have never checked off master, msdb, tempdb for each user. However, my manager insists that it should be. I have only checked off the database(s) that I wanted that user to have access to only. It was my understanding that indirectly the user had access to master, msdb, and tempdb. He wants proof of what I or he says. Can anyone point me to a web page?