"National Best Bid and Offer (NBBO) is a regulation by the United States Securities and Exchange Commission that requires brokers to execute customer trades at the best available ask price when buying securities, and the best available bid price when selling securities."
So even if you wanted to sell your Tether for $0.50 each, it'll execute at ~$1.
Most exchanges use NBBO-like mechanisms.
"National Best Bid and Offer (NBBO) is a regulation by the United States Securities and Exchange Commission that requires brokers to execute customer trades at the best available ask price when buying securities, and the best available bid price when selling securities."
So even if you wanted to sell your Tether for $0.50 each, it'll execute at ~$1.