I don't know why I've always loved this trick. It's a silly hack on using a custom currency symbol to force a percentage sign as part of the field object. I abhor "combining" textboxes and field objects within the Crystal Designer, so I like this approach.
1. Right-click on the field in question, select Format Field.
2. Click the "Display Currency Symbol" checkbox.
3. Click the "Customize" button.
4. Click the "Currency Symbol" tab.
5. Change your currency symbol from "$" to "%".
6. Then change the "Position" to "-123%".
This forces the percentage symbol to appear at the end of the numerical value.
This will give you percentages thus: "87.22%".