Note that individual states are allowed to set their own minimums higher than the Federal minimum. e.g., according to WP
-- Cali will go up to $10.55/hr starting January 1; Several other states are already above $8.
For tipped workers -- if they do NOT actually earn enough to make up the difference between 2.13 and 7.25, the business is required to pay them the difference (because these workers are taxed based on 7.25/hr)...but, it may not actually happen. tbh, if someone is working at a waiter-type job where they consistently do not really earn enough to cover that difference, they're likely better off seeking work elsewhere, as the place probably isn't getting much business at all, and/or could have managers who will refuse to make up the difference or even threaten to fire a worker for asking. Note that a few states have higher "tipped worker" minimums.
"Exempt" workers may be a special case. Also, businesses under a certain size *may* be exempt, but that is definitely a "do research for your particular state" situation.