(Reuters) -Crypto giant Tether is in talks to raise as much as $20 billion in a private placement that could value the El Salvador-based firm at about$500 billion, Bloomberg News reported on Tuesday. The company is seeking $15 billion to$20 billion for roughly a 3% stake, the report said, citing people familiar with the matter. Still, the figures were top-end targets and eventual numbers could end up significantly lower, with the valuation of the company depending on the stake offered, the report added ...