What is the main function of the Sub Penny Rule?

The main function of the Sub Penny Rule is to establish minimum pricing increments for quoting prices in securities. This rule was implemented primarily to improve market quality by preventing orders from being placed at prices that are less than a penny away from the best bid and offer. By enforcing minimum pricing increments, the rule aims to reduce market fragmentation and ensure that price quotes reflect the true value of securities more accurately, thus enhancing the efficiency of price discovery in the market.

The other options do not relate directly to the core purpose of the Sub Penny Rule. Allocating market data revenue, governing market data distribution, and prioritizing order entries are functions associated with different regulatory and operational aspects of financial markets, but they do not pertain to setting minimum price increment standards.