Expenses are handled in the following way in Web Suite or BillQuick Online:
EXPENSE CODE SETUP
First, you need to set up your expense codes for the company. You may specify a Purchase Tax on an expense code so that BillQuick knows how much GST is included.
EXPENSE ENTRY
After creating an expense code, you can use it for tracking your expenses. Example: Courier Fee including GST. When Courier is selected as the expense code, the Purchase Tax is read from the Expense screen. Enter 1 unit at $22.00 (i.e., the value on the receipt/invoice) but keep the Cost Includes Purchase Tax option checked. 
When saving, Web Suite takes off the GST and calculates the amount as $20.00. When invoiced later, the GST will be added back.
GST is added to time and expense when invoiced provided MET (Main Expense Tax) has been set up in the Project-Details screen.