I've noticed a trend (at least on the Google Play store) of application prices ending in x.99, while 'donation' apps usually end on the dollar. I see the reasoning behind the psychology that makes a user purchase a $0.99 item over one that costs $1.00, but why the trend to keep the prices on the dollar for donation items?
The psychology behind the $0.99 was explored in depth in Priceless: The Hidden Psychology of Value, which if you ask for my humble opinion, is a life-changing book. Partly the reason for such price tags is that it translates for many as a 'sale' price. Against it, is that it is typically associated with 'hard sale'.
The donation payment system is in its core anti-capitalist, thus anti-commerce, and so prices are accordingly just simple (distinguishing themselves from any sale or hard sale like prices).
I know this question is old, and the purpose of misleading prices has been covered, but I don't see any explanations about why donations are round amounts.
Simply put, taking donations as whole numbers is more convenient for charities.
They don't charge taxes or give change, so they list preset donation amounts without fractions of whole numbers (eg, cents) to make accounting easy, unless of course they accept coin donations in real life as well.
Asking for whole numbers is also more convenient for making donations. If you're using a web app to make a custom donation, it's easier to only have to enter one or two digits for the amount of dollars for example. In the real world, it's easier to only have to hand over one or two bills and maybe a handful of coins.