Accounting professionals can only ever look at user interfaces. If there is a suspicion of fraud then a court can ask expert witnesses to look into the software

Accounting professionals can only ever look at user interfaces. If there is a suspicion of fraud then a court can ask expert witnesses to look into the software itself. The law does put some constraints on what accounting software must and must not allow users to do (e.g change data without leaving a trace). But I'm not aware of any specific legal requirements regarding data representation or mandating the use of specific algorithms where mathematically equivalent ones exist.