For many mainstream new vehicles, getting below MSRP is a reasonable goal. But assigning one universal percentage to every vehicle is a mistake.
A 2% discount could be a very strong deal on a vehicle with tight supply and a small MSRP-to-invoice spread.
A 5% discount could be excellent on one model and completely ordinary on another.
And on certain vehicles with large manufacturer incentives, aging inventory or weak demand, discounts well beyond that may be available.
Don't ask only, "What percentage off MSRP did I get?" Ask, "What could this particular vehicle realistically be bought for today?"