Excel 2003 Finding most common text value

I am trying to find a formula that will calculate the most common finding the three most common job numbers used so that I can spread a discount between them. I use Excel 2003. I am sure this is very easy and I am simply having a brain fart, but if anyone could help I would greatly appreciate it. I know the file uploaded is simple, but some months is is very long. I would like to set the formulas up in the template so I don't have to do this each month.

Thanks