Is this even legal? Cash is legal tender for all debts, public and private.

Whenever I order food and services at a real restaurant (not a fast-food joint where I must pay up front), I incur a debt with the expectation that I will settle it as I leave. Can the restaurant legally refuse to accept cash as settlement for my debt, as long as I'm not using cash in a blatantly unreasonable way such as paying $250 in dollar bills?