No man, basically you want do do the following math: MSRP + taxes - discount.
In Washington, sales tax is something like 10%. So if a car costs 50k, the OTD price is 55k.
You want to shoot for something like 5-7% under that 55k, not the 50k.
I've bought 2 brand new cars so far. What you want to do is to figure out the math yourself. Like, take the sticker price, remove some off (5-7% for base model, more for loaded model) and then add back taxes.
Start the negotiation with the MSRP, ask the dealer to do the math "out the door" (incl. taxes and fees) for you and see if it matches with your own math.
If it does, then try to haggle some off from it. DO NOT go to the dealership without knowing how much you are willing to pay.
Don't go with the intention of ripping off the dealer. They aren't necessarily evil people. If they are good people, they want to sell a car and you want to buy a car, right?
They usually have good margins, so asking 5-7% isn't a lot anyway.
See this video from subaruwrxfan on YouTube:
Subaruwrxfan on how to negotiate a car deal