2015-8: Unlucky 13

You've just been hired by a new company and you've learned that the owner has triskaidekaphobia (fear of the number 13). As such he's issued a corporate mandate that no output from any program shall include the number 13 – 12.99 will be used instead. Your boss wants you to implement a function to process output and change the 13s to 12.99. For now, you need only concern yourself with numeric data and not worry about 13s that are formatted in text.