What it means
Price often turns just before them or runs just beyond them. Avoid hiding your stop right next to one.
In practice
People place orders at tidy prices. Take-profit orders, stops and option strikes gather at figures such as 1.1000 on EUR/USD or 100,000 on Bitcoin, so the market often hesitates there.
Traders use round numbers as extra confirmation for a level and as realistic targets. A first approach to a major one commonly brings a reaction.
What to watch for
Because everyone sees them, stops stack up just beyond. Placing a stop a few ticks past a big round number puts it exactly where the market tends to reach before turning.