How do you Calculate the Percentage Improvement of Percentages?

If you make 99.9930% of you possible sales in a month and your manager asked you to get a 5% improvement in the next month, what would your percentage have to be (or is this impossible...)?How do you Calculate the Percentage Improvement of Percentages?
if you are saying the absolute best score achievable is 100%, then a 5 % improvement would be 5% of the difference between 100 and 99.993 = .007, 5% of this is .00035 so the score would be 99.99335%