Pledge event administrators may enter up to five suggested donation amounts for the personal fundraising pages. These amounts show up as buttons that make donating easy on any device and prompt donors to select one of your predesignated amounts. This format works especially well for mobile devices where donors want to make donations as simply as possible. You can also suggest donation amounts that are significant for your organization (ie $108). Donors can always choose the other button and enter any amount they wish.
Go to Pledge ->Settings, here you will see the field for Suggested Donation Amounts. Enter the desired amounts here (up to five), separated by a comma and no spaces - ie 5,10,25,50,100. Buttons will appear on the personal fundraising pages for each of your predesignated amounts.