Automatic total of more than one invoices
 

In Excel 2000 General templates - Sales invoice- ( I have created sales
invoice temlpate which suites my requirement) How to get sum of TOTAL of
more than one invoices which we issue in a day. For examlple , If I issue 10
sales invoices in a day , I should be able to get the sum total of the amount
of 10 invoices automatically in a cell. What functions/ codes should I use to
achieve my requirement. At present I am mechanically adding the total of ten
sales invoices to get the sum . I would like to get the sum automatically.
Kindly help me.