foreach ($record as $data) {
  $mArray = array();
  $name = $data['user'];
  $customer = $data['customer'];
  $project = $data['project'];
  $hours = $data['hours'];

  $mArray[$name][$customer][$project] += $hours;
}

foreach ($mArray as $username) {
  foreach ($mArray[$username] as $customerName) {
    foreach ($mArray[$username][$customerName] as $project ) {
        echo '<'.$username.'><'.$customerName.'><'.$project.'><hours>'.
           $mArray[$username][$customerName][$project].'</hours></'.$project.'>
           </'.$customerName.'></'.$username.'>';
    }
  }
}

foreach ($mArray as $userKey => $username) {
  foreach ($mArray[$userKey] as $customerKey => $customerName) {
    foreach ($mArray[$userKey][$customerKey] as $projectKey => $projectName) {
      echo '<name>'.$userKey.'</name>';
      echo "n";
      echo '<customerName>'.$customerKey.'</customerName>';
      echo "n";
      echo '<projectName>'.$projectKey.'</projectName>';
      echo "n";
      echo '<hours>'.$mArray[$userKey][$customerKey][$projectKey].'</hours>';
      echo "n";
    }
  }
}

foreach($mArray as $username) {
   foreach($username as ...)

foreach($mArray as $key => $user) {
   foreach($mArray[$key] as ...)