Prices ending in ".99" had noticeably better conversion rates — as much as +117% better in one case.
"Across the board, prices ending in .99 have higher conversion rates than prices ending in one cent higher."
Here’s Gumroad’s comparison table from their write-up displaying the results of their analysis:
Are you an app developer selling in the App Store? Or maybe you’re working on a premium icon set, WordPress theme or e-book to bolster your income. This info might help you come up with a good price.
Read the entire report and their theory on why prices ending ".99" convert better in the Gumroad blog post called A Penny Saved: Psychological Pricing.