I'm sure they're really hurting for that cent, you think?

Not at all. Just explaining why there’d be a price difference. Apple has a good reason for not allowing weird prices like $3.61 but also excludes prices like $5. They also used to require that subscriptions outside the App Store match In-App Purchase prices, but dropped that requirement.

Pricing $5.99 in-app and $5 outside is a good strategy. It’s a nudge to get users to buy outside the app and save 15%, but if not they’re effectively splitting the Apple tax.

Your second paragraph explains why you think there would be a price difference. That you can only choose 4.99 or 5.99 seems unrelated to your actual theory, and it doesn't make sense on its own.