Understanding taxes and the income statement

[P M]

Very basic problem here.  I made an invoice for a service that I did.  I received $20.  Where I live I have to charge 7% tax.  So the revenue is actually $18.69 and the tax is 1.31.    My invoice has a subtotal of $18.69 and a tax of 1.31.  I post it and get it paid and for some reason my tax expense is a -1.31.  In other words my net income is boosted by $1.31 as opposed to decreased to $1.31.  Why is this?  Is this because I haven't actually paid the sales tax yet and I close it out later?


Pete