Why this matters
The bug. IEEE-754 doubles can't represent decimal fractions like 0.1 exactly. Summing them accumulates a tiny round-off, so 0.1 + 0.2 === 0.3 is false in every JavaScript runtime ever shipped.
The fix. Compare with an absolute tolerance. 1e-9 is a reasonable default for sums of consumer-scale doubles; pick something larger if you're summing thousands of values, smaller if you're inside a numerics library.
Best of all. Money should never live in a float. Stash amounts as integer cents (or millicents for high-frequency math) and use === freely. The matcher accepts the epsilon fix, but the postmortem is: stop using floats for currency.
Review heuristic
Money in a float or double is a bug. Equality on a float is a bug. Accumulation in a long-running average without a corrective term is a slow-burning bug. Each one needs a deliberate justification or a type change.
External reference: CWE-682: Incorrect Calculation.