At 25 cents per gram, the tax will cost more in enforcement than it will bring in revenue, and it won't dissuade anyone from selling or using it.
So what price would you propose an alternative?
I don't think a sin tax is a great idea in the first place with something that is as addictive as cocaine. If you make it the tax high enough to discourage use, you'll be making it high enough to provide an incentive for people to have a black market to avoid the tax. And since people are addicted they will try to get it even if it is more expensive, which could lead to crime to get the money.
From what I can find, street price for powder is generally close to $100/gram and for crack closer to $150/gram, so use that to think about what kind of tax could affect behavior.
