If the accounting module is setup properly, you can do this on your own with appropriate training (external or auto-didactic). Especially if you do not have to deal with to many entries. And it depends on the company form, as it will bring up different levels of reporting you have to provide.
If you already have a tax consultant (Steuerberater), i would talk to him at first stage. I know cases, where even the consultant was willing to perform the final postings together with the customer or even on his own after proper briefing. I guess this is not a very common way. But in that case it was the easiest way for all of the people involved.
If you do not have a tax consultant, my advise would be to get into it for your own first. Especially for getting an idea of what the tax accountant needs to cover for you.