According to the Wall Street Journal, Citigroup (C) introduced a proposal for a temporary trading system to test whether pricing certain stocks in nickels and dimes instead of pennies can bolster equity-market liquidity.

"We believe wider tick sizes would help enhance liquidity and therefore we support a tick size pilot program with such a measurable goal, one that can be evaluated at the end of the pilot program to determine its relative success or failure," said Daniel Keegan, Citi's head of equities for the Americas, in the comment letter.