I'm also in the process of closing my business.
They asked me to submit BIR Form 1905. This form is to be accomplished by all taxpayers who intend to update/change any data or information, e.g. cancellation of business registration due to closure of business.
You also need to submit the following:
1. Letter requesting for cessation of registration
2. Existing BIR Certificate of Registration
3. Inventory list of unused invoices and receipts
4. Unused invoices and receipts for cancellation (bring the physical copy)
5. ITR for the past 2 years, ITR for 2007.
6. Proof of Books of Account
I brought all the returns I have submitted for the current/past years. (BIR Forms e.g. 1701,1701Q,1601C,1601E,1604CF,1604E,2551M,Annual Registration Payment Form).
Hope this helps.