Hello Katrin,
You can give the different tax amount from the calculated one. But the reconciliation will show warning or error based on the difference amount. For the difference amount of 0.01, it will show success only.
Reconciliation run would compare the calculated and actually posted tax amount and based on the difference amount will show success/warnings/error. You need to manually verify if these warnings/error messages are due to manually overridden tax amount or a system error in the reconciliation run.
Thanks
Parveen Kumar