You're charging service fees as a conduit entity for these tickets. While the service fee is not a fixed rate, but a percentage, you would need to record each purchase at dollar amount.
To illustrate, it would look like:
Now, to your question:
How do I report this on my taxes?
You would first start out by filing your Schedule C from the eyes of the business (the money you earn at your job, and the money you earn as a business are different). Just keep a general journal with the above entry for each sale and close them down to a simple balance sheet and income statement and you should be fine. Of course, read the instructions for your Schedule C before you begin.
As always, good luck.