Add .05 X 500 and it becomes $34.95.
Maybe 5000 22s is a lifetime supply. Then add the .45s. They might collect $250 tax over 50 years on the 22s, and $20 per year from the .45s, and that is from just one person. Multiply that by all the others who would pay such a tax. Obviously this will swell state coffers to an amazing degree. We're talking tens of dollars.
I find it hard to believe that someone buying 22s in boxes of 500 could also claim that 100 rounds a Year is a reasonable usage rate. And no, we're not talking "tens of dollars" but "tens of thousands".
This tax would actually be dangerous! It would decrease safety because people will be less likely to practice at the range. We know that practice increases safety. People who don't practice may not be able to hit the intruder, or be uncomfortable with their guns. Also, ammunition becomes stale over time. While blowing off old rounds at the range is fine, you don't want to rely on them if you might need them.