First, calculates minutes, then calculate how many hours are those minutes and add them to the hours:
<?php foreach ($data as $entry) {
list($hour, $minutes) = explode(':', $entry);
$total_hours += $hour;
$total_minutes += $minutes;
}
$hours_from_minutes = floor($total_minutes / 60);
$total_hours += $hours_from_minutes;
$total_minutes -= $hours_from_minutes * 60;
echo "$total_hours:$total_minutes"