In a series of three or more terms with a single conjunction, use a comma after each term except the last.
- One, two, and three little red jelly beans fell on the floor. (Yum)
- Coffee, tea, and milk were offered to us at the haunted house.
- She bought the present, wrapped it, and hid it behind the cat box.
When it comes to the names of business firms, the last comma is usually omitted. Follow the example of the establishment.
- Smith, Mercurio and Co.
Having fun with this? Information gathered from Elements of Style.
Happily ... after retirement 
My edition of The Elements of Style (1972) gives the rule that you repeat, however the examples are as follows:
red, white, and blue
gold, silver, and copper
He opened the letter, read it, and made a note of it’s contents.
These examples make clear that the rule’s “except the last” refers to the last term in the series, i.e. in the examples “blue,” “copper,” and “contents.”
You have not followed this rule in the examples you provide.
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I appreciate this comment. I’ve always had trouble with adding that last comma … it never felt right to me. However, I will get over the ‘feeling’ and do it as you suggested.
With appreciation — Marge
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