Calculating percent of total with select all questions in Tableau

Question

I am working with survey data and using Tableau to create visualizations. There are some select all questions such as ("Why didn't you purchase item x? select all that apply"). The way the data is collected, there is a unique identifier id for each respondent and if a respondent chooses multiple answers for the select all, it goes into one cell. For example, for the above question, the response could be "too expensive, need to think about it". However, when I visualize it, I want too expensive and need to think about it to become separate bars and calculate each as a percentage. I have been successful in separating them and creating dummy columns but I can't seem to calculate the percent of the total using the different rows. How can I do this?