Security trading now fragments into more than 10 almost identical stock exchanges in the United States. We show that discrete pricing is one economic force that prevents the consolidation of trading volume. The uniform one-cent tick size (minimum price variation), imposed by the SEC's Rule 612,...

Stock exchange operators compete for order flow by setting "make" fees for limit orders and "take" fees for market orders. When traders quote continuous prices, they can choose prices that perfectly neutralize any fee division, and traders stream to the exchange with the lowest total fee. The...