Thanks for reaching out to the Community forum, xunz27.
Right now, Luxury Car Tax (LCT) is not determined by QuickBooks, so reportable amounts have to be determined manually or another fashion. LCT is paid based on the same period required for GST reporting, which in QuickBooks is usually the Business Activity Statement (BAS).
For guidance in recording GST, LCT, stamp duty for car purchase on QuickBooks, I recommend consulting a Tax Professional. This is to ensure that amounts are properly recorded.
You can also visit below links to explore ATO websites: