Calculating column and row sum in html table using jquery selectors

If you want to prevent the bottom-left and bottom-right cells in the table from displaying the total (at least this is how I understand your question), you'll have to change your selector from #sum_table tr:last td to #sum_table tr:last td:not(:first,:last). And then, to account for the shift in indices (since the td element in column 1 has been excluded), you'll have to change ++i to i+2. Here's an updated version of the second part of your JS code (JSFiddle):

$("#sum_table tr:last td:not(:first,:last)").text(function(i){
    var t = 0;
    $(this).parent().prevAll().find("td:nth-child("+(i+2)+")").each(function(){
        t += parseInt( $(this).text(), 10 ) || 0;
    });
    return "Total: " + t;
});

Edit: Based on the update you made, is this perhaps more in line with what you're after? This solution basically modifies the HTML code by switching the second-last and last td's in each tr (i.e., in each row), and the first CSS selector in the JS code was modified to #sum_table tr:not(:first,:last) td:nth-child(5) so that the "Total" gets displayed in the second last column (i.e., the 5th td of each applicable row).

If, for whatever reason, you want the HTML code to stay as is and you'd like to implement a purely-JS solution that doesn't involve modifying the HTML code by hand, you can do something like the following (JSFiddle):

//Swap the second-last and last columns
$("#sum_table tr td:last-child").each(function(){
    var lastRowContent = $(this)[0].innerHTML;
    var secondLastRowContent = $(this).parent().find("td:nth-child(5)")[0].innerHTML;
    $(this).parent().find("td:nth-child(5)")[0].innerHTML = lastRowContent;
    $(this)[0].innerHTML = secondLastRowContent;
});

$("#sum_table tr:not(:first,:last)  td:nth-child(5)").text(function(){
    var t = 0;
    $(this).prevAll().each(function(){ 
        t += parseInt( $(this).text(), 10 ) || 0;
    });
    return t;
});

$("#sum_table tr:last td:not(:first)").text(function(i){
    var t = 0;
    $(this).parent().prevAll().find("td:nth-child("+(i+2)+")").each(function(){
        t += parseInt( $(this).text(), 10 ) || 0;
    });
    return "Total: " + t;
});

This is basically the same as the first solution presented above in this edit, except the second-last and last columns are swapped programmatically using jQuery (instead of being manually swapped by hand).