Finally, my Tips calculator app is in App store. Check it out:
Wonder how much tip you should give? Looking for a way to come up with the tip based on the satisfaction of service quickly? This app is your solution! This FREE intuitive app helps anyone to calculate the tip based on how satisfy you are with your service and split the bill for your party. All you need is to provide the total bill (including tax!)
On top of it, you can set your tax rate for your neighborhood! You can also round up the total+tips to the closest .50 cents if you preferred! And you can customize the base tip rate, maximum tip rate for every user!
http://itunes.apple.com/app/tipstor/id439571466?mt=8