Is SQL Injection possible in this PHP registration script?

I've recently created a PHP registration script for a website that a friend and I are working on. I've read up on the dangers of MySQL injection, and I was wondering if my current code is protected from such attacks, or if additional steps need to be taken.

The relevant part of the code is as follows

  $email = $_POST['email'];
  $username = $_POST['username'];

  $username = strip_tags(trim($username));
  $email = strip_tags(trim($email));

  //Sanitation code I found somewhere..
  function mres($var){
    $conn = get_my_db();

    if (get_magic_quotes_gpc()){
        $var = stripslashes(trim($var));
    }
    return $conn->real_escape_string(trim($var));
  }

  //Sanitize username
  $sanUsername = mres($username);

  //Make SQL query
  $sql = "SELECT username FROM accounts WHERE username = '$sanUsername' ";
  $result = $conn->query($sql);

Thanks in advance,

Shawn