We really sell products here with GST included. No customer wants to calculate tax costs on top of the purchase price. They want to look at what it costs and know, instantly; “That’s what I have to pay”. GST is my business. A customer isn’t interested in business tasks.
Is there any way I can do that when applying a tax rate?
When configuring a product, you can set the tax rate against the product.
There is no such option under product.
Furthermore, neither is there such an option when setting up tax rates.
Unless, I’m blind 
Hence, taxes are always being “added”, never included.
What I wanted is; Say I setup a 10% GST tax rate,
if I sell a product for 9 bucks, the GST should be included, speak, the 9 bucks reflect the product price inclusive the 10% GST
Update:
I just noticed,
on the actual quote/invoice, I can declare Tax = None, despite the product has a 10% tax rate.
[A] this doesn’t make 100% sense to me.
If product has a 10% tax rate attached to, that 10% tax should automatically be placed into the quote/invoice and it shouldn’t be able to be taken off!
[B] is that the feature you’d referred to, then this isn’t correct neither because if GST needs to be added (here in Australia if you’re GST registered, GST literally applies to every product you’re selling), then the GST need to be shown on Quote/Invoice.
Uhm, I hope I make sense?!
Nothing, Not anything?
The process is to put in a formal request via the request system and get other users and developers to discuss and vote on this. There are a number of requests, some of them dating back some time, These then gets priorities according to the urgency, complexity, availability of resources and so on. The developers will word from the approved list of issues and requests, not the forums.
I would therefore suggest you add a feature request.