I"m assuming since you're asking on a workplace site, that a technological solution is not feasable. You're going to need to motivate people.
Nobody is Perfect Humans make mistakes. Requiring unachievable goals will just make people give up. If you're not satisfied with 99% I may as well give you -90%.
You don't get something for nothing Are they in a hurry? Do they get negative feedback for not keeping up with a quota. Being sloppy with the inventory counts may be just one way to cut a corner.
Who Cares? Do they really know how important this is? Will you give them the time to do it right?
What's in it for me? Since you seem to be able to count the inventory after the fact (How else did you know the counts were off?), maybe you can create an incentive program for a team/group/shift to keep accurate counts.
Just Ask Approach people and ask what can be done about this. You'll probably learn something about the people.
Edit: Along with the motivational aspects of the data entry problem, there may be some other solutions. Using a scale to get an accurate measurement of partial rolls. The period key may be broke. Then again, maybe they just need to take their gloves off.