You'll want to take an Autosomal DNA test to get percentages like that. Family Tree DNA's Family Finder test will provide this information. It can go back 5 generations with relative confidence, sometimes further back.
I'm giving a free webinar (web-based seminar) -- Genetic Genealogy for Beginners -- on Tuesday, March 1. It will discuss the different types of tests available through Family Tree DNA. If you're interested in attending, please visit my website for more information and to register - http://www.relativeroots.net/webinars/
You want either the Family Tree DNA Family Finder test which includes Population Finder tool or the 23andMe test which includes an Ancestry Painting. You can see screenshots on these pages:
I would recommend the Family Finder test if you are interested in testing for genealogical matches. The 23andMe test is primarily a health test but is very interesting nonetheless.
An mtDNA test only follows the direct maternal line:
An mtDNA test can give you much better geographical resolution than an autosomal DNA test. There are for instance a number of haplogroups which are associated with Native American ancestry. This will of course only be picked up if the Native American ancestor is on the direct maternal line.
If you are interested in Y-DNA testing you would need to find a male relative to take a test for you through a surname project. Females do not have a Y-chromosome.