Not even a penny?
Why bother? If you donate a penny and you're a billionaire you come off looking like a straight starfish, I can see the headline now: "Billionaire donates one cent to autism research."
Nobody's gonna publish a title saying "Billionaire doesn't donate to foundation" unless you're asked to by that foundation and refuse.
As a billionaire, your primary concern is PR. Billionaires donate to improve their public image. Donating small amounts as a billionaire makes you seem more greedy than not donating at all.