If you have a small practice and have been operating without GST and now have grown and need to register for GST then you need to do three things:

1. Set the tax at the practice level - see also http://www.openvpms.org/documentation/csh/1.8/concepts/taxes
2. Adjust the invoice and credit document contents so that they say 'Tax Invoice' and show your ABN
3. Adjust all your prices to account for the fact that you will be paying GST to the Government.

The last is most easily done using the Price Export/Import facility - see http://www.openvpms.org/documentation/csh/1.8/concepts/pricingUpdates

ie export all the prices, push them up by 10% (or whatever) and import the updated data.

Note that if you are running 1.7 then you can use the 1.7 versions of the above (just by changeing 1.8 to 1.7 in the URL).

Regards, Tim G