As far as I am aware, this was the second third-party application ever available for Palm WebOS (and Dali Clock was the third).
By default, the Tip Calculator only does whole numbers, because if you insist that your tip be accurate to the penny you are a cheapskate weirdo. Here in the Colonies, we use paper money, not coins. If your bill is $44.22, just enter $45. Don't go all Scrooge McAsperger's on us, ok? But, there is a "scrooge mode" that lets you calculate your tips so that no penny is left behind, if that is how you roll.
I tried to get Tip Calculator into Palm's App Catalog, but dealing with their app-submission process was a Kafka-esque nightmare, and so I gave up on Palm WebOS development shortly after writing it.
If you still have a Pre, you can install it via Preware, which is an installer for many third-party packages. After installation, it can be found under "Applications/Finance".
Alternately, if you have the WebOS development kit you can just install it from the command line over USB by doing: