Hi leighton2,

Thanks for posting in the Community! If you are needing to record another amount for GST that is not 10% you can set the transaction to Exclusive of Tax and manually change the amount to what you need. Here's how:

1. Open a bill.
2. On Amounts are, select Exclusive of Tax.
3. Enter bill details.
4. After you select a GST rate on a transaction, you'll see a small box where you can enter a GST amount. 
5. Select Save.

You can also check this article for more information: Check how much GST you owe in QuickBooks Online.

Feel free to drop a comment below if you have any other questions. I'll be around to help.