I'm sure that most of you who pay taxes on the parts they purchase have considered charging your customers for said tax, but think it would be rude. Well, I'm here to put your mind at ease and help you out a little bit. Profit Rhino has a feature that will allow you to automatically apply tax to those parts without creating a separate line on the invoice or anything like that, it will just add the tax onto the total price.
So not only will you no longer be losing money on tax, your customers won't feel like they're being charged for something extra.
It's pretty simple to do, so I'll just post the following image to explain it:
TAXES IN BUSINESS INFORMATION
The image breaks down what each section means and how you'll do it. Just to reiterate though, you can set a tax on labor and parts if you want (I wouldn't set one on labor if I were you), you can have that tax apply to the cost of buying that part, or the retail price you're selling it for, and you can set whatever tax rate you like.
So what I recommend is that you charge a tax on the cost, set your state tax rate, and then hit [Calculate Biz Info] and you should be all set. Good luck.