The market cap goes down. The company has less cash, and that cash was priced into the market cap. If you yourself had a a market cap of $25 including the $5

The market cap goes down. The company has less cash, and that cash was priced into the market cap. If you yourself had a a market cap of $25 including the $5 in your wallet, giving away that $5 would lower you market cap to $20.