Use the level of precision the business decision actually needs. In most case calculations, carrying many repeating decimals creates extra work without improving the conclusion.

State the approximation when it matters: "I will use 33.3%" or "roughly one third." That keeps the math transparent and prevents later differences from looking like accidental errors.

If the number feeds several later calculations, keep one sensible extra decimal until the end. If it is only used to compare options, a cleaner approximation may be enough.

The key is consistency. Round deliberately, not randomly, and interpret the result in business terms. The mental math guide includes more on efficient case calculations.

I say the approximation out loud and move on. Carrying six decimals just creates more ways to mess up.