A tax invoice / receipt will normally be included in the PDF that is sent to your email address when you purchase tickets and when prompted to download your tickets when you purchase them. You'll find the receipt as the final page after your tickets.
If you need to get a tax invoice / receipt for your ticket purchase again, it can be easily obtained from your My Eventfinda account.
Simply login to Eventfinda and go to My Eventfinda. You'll see a list of your ticket purchases there with a button to Download Receipt next to the event name.
Click that button and your receipt will be downloaded and available to print.