Sum function

I have an excel worksheet I use for Invoices to bill customers. When I sum the page, the rounded numbers are not added. Instead excel is adding the longer decimal version of the number which is causing my invoice totals to be a few cents off.

For example: 

40*24.92+2.75*37.38+10*49.84 =

And When I round up that number becomes 1,598.00 which is the number I want excel to add but instead it adds the longer version. I have been manually adding them with a calculator and typing in the correct sum. Is there any way to have excel add up my invoice amounts as shown.