One reason I'm aware of is for foreign customers who are buying in foreign currencies.
As a developer, I don't want to set prices in every currency, so they translate the price grid for me which I found useful.
Prices on eBay actually look like something a human would choose. On AliExpress on the other hand the prices are all over the place, with really odd numbers of cents, which I assume comes from automatic conversion from whatever currency they initially priced it in (not necessarily dollars at that point).
In any case, actually probably have such rules, just not public. I am sure they have sales people being paid full time to agonise over such issues.