Calculate Row and Grand Total in GridView on Tab Key Press using JavaScript

hi friend i am developing a web application,in that application i want to do a calculations like total salary,basic salary,pf,hra etc.....in that i provide a button for calculate.if i click that button the value will be calculated and displayed in the textbox..but i dont want to do that,,i want to do like ...when i press the tab key it will be calculated and show in textbox.how this is possible?