Microstructural phenomenons: option strikes

There's no such thing as round levels, instead:
1) You open the option chain of given vehicle;
2) You notice the step between the strikes that have significantly higher volume/OI than the other ones;
3) for example on ES dem would be xx50.00 and xx00.00;

Without further analytics of the option chain, the very general rule is that these levels usually stop & repel the sharp jumps in prices, and allow the average activity to pass through em with a little stuck around em.

Again the reason is microstructural, some of are hedging current & anticipated option positions on good prices. Usually market allows to do it right after economic releases.

About the example, if you have any platform that offers a liquidity heatmap, try to find that reversal on ES & correlated assets, that moment in time that I market with a circle, you might be surprised.