Are you selecting a rounding method on the sales invoice input screen?
Also, the desktop version of Manager is always free forever and is the full version, unlike most competing programs that only give you a trial period or limited capability. The only versions you pay for are the server version and the cloud version. But the difference is in access, not capability or features.
Could you show some screenshot how you are recording these amounts and what you see? I’m not really sure how you have determined VAT is 26,569 € (not saying it’s incorrect)