Airflow over/around a car is even more predictable than an aeroplane. There is a much smaller speed range, and no change in angle of attack to worry about.
However the back end of a car is so blunt that there is not a hope of the airflow sticking to the surface beyond the boot lid . The Austin Allegro was famously proven to be more aerodynamic backwards than it was forwards - a fact often touted by the presenters of Top Gear. Actually, the same applies to most, if not all motor cars, especially estates.
For best aerodynamics, the depression behind a car that causes most of its drag, should be filled in thus:
Not sure why this hasn't caught on! But in its absence, the best that can be done for that depression behind the car is to minimise it. This is done by deflecting the air sharply upwards as it leaves the boot lid, thus tightening the air-curl and dissipating its energy much closer behind the car, rather than leaving a long trail of eddies way behind the vehicle. That's why you often see the bootlid spoilers like these:
It is a flow-trip device of sorts, but is to dissipate the energy in the airflow more quickly, and over a shorter distance, rather than try to make it stick to any surface.
Don't expect to see dimples on car or aeroplane skins any time soon. They are a blunderbus approach to flow tripping, and most inefficient at that. They are a drastic compromise given that most other flow-trip devices wouldn't tolerate the repeated impact from a 5-iron.