Tipping is part of casino etiquette and doesn’t matter is it a land-based casino or an online Ethereum casino. They are optional, but of course welcome. The amount depends on your bets. It is considered good practice to leave a tip after 20-30 played rounds. If the game is over for you quickly, you lose, then their size may be small. In case of big wins at Ethereum blackjack, a little more should be left.