Cook County is proposing a $25 per gun tax on the purchase of firearms within Cook County to alegedly pay for the death, destruction, and mayhem they cause there. Frankly anyone who would be able to purchase a gun in Cook county is probably not going to use it to commit a crime.
This is not to say they might be buying it for someone who will, bit nobody's crystal ball is that good.
Here is Colorado we're going to get pretty much the same thing as private purchases now require a background check at a minimum cost of $10 to be paid to the CBI, who then uses the NICS system for free and relays the info back eventually. No word yet as to how much the gun shops will be allowed to add to this to cover their costs, but I'm guessing between $20 and $35 on top of the $10.
The purpose of gun laws has historically been to keep firearms out of the hands of undesirables, namely the poor blacks and whites. Tacking on a stiff tax is an easy way to do this without appearing to single out any one group. Just the ones on the bottom of the food chain who probably need the protection the most.