Calcula o troco de um determinado valor

troco.php

<?php
function modulo($num1, $num2 ){
	$result = (($num1 / $num2) - floor($num1 / $num2)) * $num2;
	return (float)number_format($result, 3, '.', '');
}
function calc_troco($pago, $conta){ 
  
  $nota = array('100', '50', '10', '5', '1');
    $centavos = array('50', '10', '5','1');
	$troco = $pago - $conta;
	$vlr = $troco;
	for($i = 0; $i <= 4; $i++){
		$ct = floor($vlr / $nota[$i]); // calculando a qtde de notas
		if ($ct) {
			$result = $ct. " nota(s) de R$". $nota[$i]." Reais<br>";
			$vlr = modulo($vlr, $nota[$i]); // sobra
			echo $result;
		}
	}
	$vlr = $vlr * 100;
	foreach($centavos as $cent){
		$ct = floor($vlr / $cent);
		if($ct){
			$result = "$ct moeda(s) de {$cent} centavos<br>";
			$vlr = modulo($vlr, $cent);
			echo $result;
		}
	}
}
calc_troco(20, 5.20);