sum of textboxes with javascript and using comma instead of dot in decimal numbers

I found a code block on the web that does the sum of textboxes. This block of code looked exactly what I was looking for, but I need to use commas instead of dots, and I even need to prevent the entry of periods in textboxes. unfortunately my javascript knowledge is very amateur and i don’t know how to do this. can you help me with this
thanks

<html>
    <head>
        <title>Sum Html Textbox Values using jQuery/JavaScript</title>
        <style>
            body {
                font-family: sans-serif;
            }
            #summation {
                font-size: 18px;
                font-weight: bold;
                color:#174C68;
            }
            .txt {
                background-color: #FEFFB0;
                font-weight: bold;
                text-align: right;
            }
        </style>
        <script src="https://ajax.googleapis.com/ajax/libs/jquery/1.7.1/jquery.min.js"></script>
    </head>
    <body>
<table width="300px" border="1" style="border-collapse:collapse;background-color:#E8DCFF">
    <tr>
        <td width="40px">1</td>
        <td>Butter</td>
        <td><input class="txt" type="text" name="txt"/></td>
    </tr>
    <tr>
        <td>2</td>
        <td>Cheese</td>
        <td><input class="txt" type="text" name="txt"/></td>
    </tr>
    <tr>
        <td>3</td>
        <td>Eggs</td>
        <td><input class="txt" type="text" name="txt"/></td>
    </tr>
    <tr>
        <td>4</td>
        <td>Milk</td>
        <td><input class="txt" type="text" name="txt"/></td>
    </tr>
    <tr>
        <td>5</td>
        <td>Bread</td>
        <td><input class="txt" type="text" name="txt"/></td>
    </tr>
    <tr>
        <td>6</td>
        <td>Soap</td>
        <td><input class="txt" type="text" name="txt"/></td>
    </tr>
    <tr id="summation">
        <td>&nbsp;</td>
        <td align="right">Sum :</td>
        <td align="center"><span id="sum">0</span></td>
    </tr>
</table>
<script>
    $(document).ready(function(){
 
        //iterate through each textboxes and add keyup
        //handler to trigger sum event
        $(".txt").each(function() {
 
            $(this).keyup(function(){
                calculateSum();
            });
        });
 
    });
 
    function calculateSum() {
 
        var sum = 0;
        //iterate through each textboxes and add the values
        $(".txt").each(function() {
 
            //add only if the value is number
            if(!isNaN(this.value) && this.value.length!=0) {
                sum += parseFloat(this.value);
            }
 
        });
        //.toFixed() method will roundoff the final sum to 2 decimal places
        $("#sum").html(sum.toFixed(2));
    }
</script>

jsfiddle link