When there are three or more terms in a single conjunction, use a comma after each term except the last. For example:
pears, oranges, and apples
blue, purple, and gold
The only time when this rule isn't followed, is when companies choose to omit it themselves. For example:
Wiseman, Wiseman and Wiseman
Jones, Brown and Deloitte
In this case, see how the company has chosen to write it and follow their lead.