I had a conversation with the State of Georgia tax collector today. Turns out the regional property tax collection office is in Cartersville, GA, where my RV-6 is based and also where I work. My RV-10 isn't registered and won't be for a couple of months, at best. I was just trying to do some cashflow planning for when taxes are due.
Here's what he said:
The State of Georgia generally receives notification of an airplane registration from the FAA about a month after you register the airplane. Following that, the state sends you a tax notice and you have 30 days to respond.
Anything you buy new from a commercial source will be taxed. If you have already paid State of Georgia sales tax on it, keep the receipt for your records. You won't have to pay twice. This includes taxed items you bought from Vans, Aircraft Spruce, Home Depot, or the local hardware store.
Items you bought from out of state, but didn't pay Georgia sales tax on will be taxed at your home county's tax rate. The engine I purchased from BPE would fall into this category.
Items you bought from an individual (i.e. "casual sales") will not be subject to sales tax. That would be things like a second hand tail kit or a used engine you bought from an individual. It helps to have receipts for these items.