Polymarket displays prices in whole cents, but the underlying on-chain settlement uses 6-decimal USDC math. Systematically take fills where that rounding of size-times-price tips in your favor (buying just under a cent boundary, redeeming or merging at an exact $1.00) to skim sub-cent residuals, repeated at high volume. The edge is the quantization mismatch between the penny-tick display and the more precise on-chain settlement.
Markets on Polymarket where fractional-cent rounding edge is the natural play: