Unfortunately the % is a mathematical calculation based on t
he votes received, so there is not a way to force it to add up to a particular number. If more than one item is rounded up you will see a total that is greater than 100% and if multiple items are rounded down you might see 99%.
Here are two examples:
If you have 30 voters and 10 vote option 1, 10 vote option 2 and 10 vote option 3, the result would be be 33.33 for each answer. These would all round down to 33%, so your total on the slide is 99%.
If you have 30 voters and 2 vote for option 1, 14 vote for option 2 and 14 vote for option 3, the results would be 6.67%, 46.67%, 46.67%. These results would be rounded up, so the results on the slide will be 7%, 47% and 47% and the total is 101%.
To make this easier for people to understand, you may wish to show the decimal places on your graphs. In the editor for each slide you will need to go to the Graphing tab and change the decimal place setting to 2 rather than 0 which is the default. The box you need to change is highlighted in blue in the below image.
