Atm Machine logic in php

<form  method="post">
<div align="center" style="width:60%;">
<b>Atm Machine Test Page</b>
<br clear="all"><br clear="all">
<div align="left" style="float:left;margin-left:200px;width:20%">
Input::
</div>
<div align="left" style="float:left;margin-left:10px;width:30%">
<input type="text" name="txtAmount" value="<?=$_POST['txtAmount']?>"/>
</div>
<br><br>
<input type="submit" name="btnGenerate" value="Generate"/>
</div>
</form>
<?php

if($_POST['btnGenerate']=="Generate")
{

 $txtAmount = $_POST['txtAmount'];
 if($txtAmount != "")
 {
 //$txtAmount= intval($txtAmount);
 $rupees = array(1000,500,100,50,20,10);
 $count = array(0,0,0,0,0,0);

 if($txtAmount <=0)
 {
 $output="<b>Invalid Amount</b>";
 }else{

 if(!preg_match('/\d\d[0]$/',$txtAmount))
 {
 $output="<b>Invalid Amount</b>";
 }else{
 for($i=0;$i<count($rupees);$i++){
 if($rupees[$i]<$txtAmount || $rupees[$i]==$txtAmount){
 $count[$i]=intval($txtAmount/$rupees[$i]);
 $txtAmount=$txtAmount%$rupees[$i];
 }
 }
 for($i=0;$i<count($count);$i++){
 if($count[$i]!=0){
  $output .= "<br><b>".$rupees[$i]." X ".$count[$i]." = ".($rupees[$i]*$count[$i])."</b>";
 }
 }

 }
 }


 }else{
 $output="<b>Invalid Amount- Amount Input Not Blank</b>";
 }
?>
<div align="center" style="width:60%;">
<?php

echo "Output: $output";
?>
</div>
<?php
}
?>

<div style="float:right;margin-right:530px;margin-top:200px;">
<h5>Developed By Sunny J Soni</h5>
</div>

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Input - 5680

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Output: 

1000 X 5 = 5000

500 X 1 = 500

100 X 1 = 100

50 X 1 = 50

20 X 1 = 20

10 X 1 = 10