Round when it materially simplifies the calculation and the case does not require high precision. The goal is to preserve the business conclusion while reducing unnecessary arithmetic.

Build a short checking habit into your process. Before you say the final number, pause for one beat and ask yourself whether the magnitude makes sense, whether the sign is right, and whether you kept track of units correctly.

Targeted practice usually beats random practice. Focus first on the operations that appear constantly in cases: percentage changes, multiplication shortcuts, division, weighted averages, and break-even style calculations.