TD Ameritrade Holding Corp. will reimburse about $10 million to customers to settle Securities and Exchange Commission charges that it misled them about the safety of a money market mutual fund.

The SEC announced the settlement Thursday after accusing TD Ameritrade of failing to reasonably supervise sales representatives who mischaracterized the Reserve Yield Plus Fund as being as safe as cash or having guaranteed liquidity.

Money market funds are designed, but not guaranteed, not to lose principal and to maintain a $1 per share net asset value. The Reserve fund “broke the buck” in September 2008 because of large redemptions and an investment in Lehman Brothers Holdings Inc., which went bankrupt.

TD Ameritrade did not admit wrongdoing in settling. It did not immediately return requests for a comment.