Kata

Complete the function, which calculates how much you need to tip based on the total amount of the bill and the service.

You need to consider the following ratings:

• Terrible: tip 0%
• Poor: tip 5%
• Good: tip 10%
• Great: tip 15%
• Excellent: tip 20%

The rating is case insensitive (so "great" = "GREAT"). If an unrecognised rating is received, then you need to return:

• "Rating not recognised" in Javascript, Python and Ruby...
• ...or null in Java
• ...or -1 in C#

Because you're a nice person, you always round up the tip, regardless of the service.