User wants to enter an expense in BillQuick and then manually enter the tax amount. For example, total expense on meals before tax = $100, GST = $2 and total expense = $102. User needs to have the tax split out so as to claim back the GST.
There is no need to enter the expense and tax amount as separate line items in Expense Log. This is what you can do:
1. Set the Purchase Tax in the Expense Codes screen for the desired expense item. Purchase Tax is the tax paid by the company on an expense item and is subtracted from the charge amount to avoid double-taxation for the client. BillQuick uses the Purchase Tax Rate to segregate the actual cost of an expense and its tax amount (Cost Amount = Net Cost Amount + Purchase Tax Rate). 
For example, you can set up an expense with a purchase tax of 12%. Later when you enter the actual expenses, BillQuick will back out 12% from the charge amount to avoid double taxation for the client (You might have already set up GST on the project in the Project-Billing screen).
2. Once the purchase tax is set up, you can show the Purchase Tax column in the Expense Log screen from the Field Chooser.
3. Check the 'Cost Includes Purchase Tax' option if your cost amount includes the tax paid by you on purchases/expenses. BillQuick prefills the Purchase Tax % based on what is set in Expense Codes.
4. You can run the Tax Tracking report from the Report Center to see the GST paid and collected.