@zneak is correct. mysql_connect does pool connections. The question is, why do you want to close the connection? In all my years of developing in PHP, I can count on one hand the number of times that I have used mysql_connect, I almost exclusively use mysql_pconnect
From http://php.net/mysql_pconnect —
Establishes a persistent connection to a MySQL server.
mysql_pconnect() acts very much like mysql_connect() with two major differences.
First, when connecting, the function would first try to find a (persistent) link that's already open with the same host, username and password. If one is found, an identifier for it will be returned instead of opening a new connection.
Second, the connection to the SQL server will not be closed when the execution of the script ends. Instead, the link will remain open for future use (mysql_close() will not close links established by mysql_pconnect()).