Something

<?php
	$total = 300;

	echo calculate_shipping($total);
	function calculate_shipping($total) {
		$shipping = 10;
		if ($total >= 100) {
			$additional = floor($total / 100) - 1;
			echo "additional:$additional\n";
			$shipping = $shipping + $additional;
		}
		return $shipping;
	}
?>