Good question, although it was more about convert than about ceiling.

A link to the msdn page for convert and decimal:

http://msdn.microsoft.com/en-us/library/ms187928(SQL.90).aspx (convert)

http://msdn.microsoft.com/en-us/library/ms187746.aspx (decimal/numeric)

The last page describes the gotcha of this question in the explanation of the scale.