GST in NZ is currently 15% not 12.5% as it currently defaults to in Reckon
All new Reckon Accounts versions default to 15% as per the legislation change on Oct 1 2010. It is possible that you are not on a recent version of Reckon Accounts, or your file was created prior to Oct 1 2010, meaning you will need to create new tax items to account for the change, and make the old codes 'inactive' so they are no longer available for selection.
Creating a new GST code in a current version of Reckon Accounts will show the tax rate below.