That is a decision you make rather than a number the software fixes. The share of charge lines that reaches a person is set by how the audit workflow is configured, and across live deployments it runs from under one line in five hundred to roughly one in three. The spread is not a difference in accuracy. It is three different answers to the same question.
One operation wanted the fewest possible items reaching its operations managers, so price differences below a set money threshold clear automatically. Fewer than two charge lines in every thousand now reach a person.
A second maintains its own rate cards and knows there is drift between what it negotiated and what the system holds. It approves no overcharge automatically, because each deviation is what finds that drift. About one line in eight is reviewed, and that is the purpose of the deployment rather than a cost of it.
A third buys largely from providers who work without rate cards, so those movements arrive with no contracted price to verify against, and the team reviews them deliberately.
So a straight-through percentage tells you very little on its own. Ask whether the threshold is yours to set, ask which unit the percentage is measured in, per invoice or per charge line, and ask what happens when you want to see more rather than less.