How get total sum from input box values using Javascript?

I am not perfect in Javascript.. I want to show total sum of values entered in qty input boxes in next input box named total without refreshing page. Can anyone will help me to figure it out..?

Here is javascript

 <script type="text/javascript"> 
 var howmanytoadd = 2;
 var rows;

 function calc() {
     var tot = 0;
     for (var i = 0; i < rows.length; i++) {
         var linetot = 0;
         rows[i].getElementsByTagName('input')[howmanytoadd].value = linetot;
         tot += linetot;
     }
     document.getElementById('total').value = tot
 }
 onload = function () {
     rows = document.getElementById('tab').getElementById('qty1');
     for (var i = 0; i < rows.length; i++) {
         rows.getElementsByTagName('input')[i].onkeyup = calc;
     }
 }
</script>

Here is my html code:

Qty1 : <input type="text" name="qty1" id="qty"/><br>
Qty2 : <input type="text" name="qty2" id="qty"/><br>
Qty3 : <input type="text" name="qty3" id="qty"/><br>
Qty4 : <input type="text" name="qty4" id="qty"/><br>
Qty5 : <input type="text" name="qty5" id="qty"/><br>
Qty6 : <input type="text" name="qty6" id="qty"/><br>
Qty7 : <input type="text" name="qty7" id="qty"/><br>
Qty8 : <input type="text" name="qty8" id="qty"/><br>
<br><br>
Total : <input type="text" name="total" id="total"/>

here is screen shot

Try:

Qty1 : <input onblur="findTotal()" type="text" name="qty" id="qty1"/><br>
Qty2 : <input onblur="findTotal()" type="text" name="qty" id="qty2"/><br>
Qty3 : <input onblur="findTotal()" type="text" name="qty" id="qty3"/><br>
Qty4 : <input onblur="findTotal()" type="text" name="qty" id="qty4"/><br>
Qty5 : <input onblur="findTotal()" type="text" name="qty" id="qty5"/><br>
Qty6 : <input onblur="findTotal()" type="text" name="qty" id="qty6"/><br>
Qty7 : <input onblur="findTotal()" type="text" name="qty" id="qty7"/><br>
Qty8 : <input onblur="findTotal()" type="text" name="qty" id="qty8"/><br>
<br><br>
Total : <input type="text" name="total" id="total"/>


    <script type="text/javascript">
function findTotal(){
    var arr = document.getElementsByName('qty');
    var tot=0;
    for(var i=0;i<arr.length;i++){
        if(parseInt(arr[i].value))
            tot += parseInt(arr[i].value);
    }
    document.getElementById('total').value = tot;
}

    </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));
	}

body {
				font-family: sans-serif;
			}
			#summation {
				font-size: 18px;
				font-weight: bold;
				color:#174C68;
			}
			.txt {
				background-color: #FEFFB0;
				font-weight: bold;
				text-align: right;
			}

<script src="https://ajax.googleapis.com/ajax/libs/jquery/1.7.1/jquery.min.js"></script>

<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>