No they don't, this is tax fraud and illegal. Companies are not allowed to claim donation round-ups as their own for tax purposes. They may match donations, which they can claim, but they cannot claim money they did not spend as their own donations. You, however, can, if you keep your receipts.

"Just because it's illegal doesn't mean they don't do it" -- Fair point, but this is the IRS we're talking about. I doubt big business are willing to fuck around that particular avenue. Other avenues, definitely.