Round up by 30 minutes

$minutes = 153; // 153 == 5*30 + 3
// How many x30 minutes fit in $minutes
$whole = intdiv($minutes / 30); // For 153: intdiv(153, 30) == 5
$remainder = $minutes % 30; // Always 0..29; For 153: 153 % 30 == 3
$roundedMinutes = $whole * 30; // For 153: 5 * 30 == 150
if ($remainder > 0) $roundedMinutes += 30; // For 153: += 30 == 180