departmental grey areas, who's responsibility?

As NAV is an ERP system where all the departments are using and sharing, there are often grey areas where each department think that this is the job that other departments should be doing. However, any inaccuracy done by one department will often affect other departments. And because they are pushing what they see as extra work not under their responsibilities, the IT department will almost always end up requiring to do all these for them just to ensure the data integrity is in the system.

For example, when creating new customer or vendor cards, the sales and project departments will said that finance department should be the one filling up all the varies posting groups in these cards since these are financial fields only finance department understand. However, finance department will push back that these are quite standard and end users should just fill these up themselves.

Another example, sales departments want finance departments to post deposit type so that they can keep track of varies deposit received. However, since deposit does not affect G/L and year end auditing, finance departments will response that since it is the sale departments who required these info, and the finance departments do not need these info, sales departments should be the one posting these entries into the system.

How do you guys manage and get all these departments to understand and work for the common good?