In 2014, the Navajo Nation Council passed the Healthy Diné Nation Act (HDNA), a 2% tax on unhealthy foods and beverages and a waiver of the 5% sales tax on healthy foods and water, to support health promotion and disease prevention among the Navajo people. Very little research has assessed implementation accuracy of food or beverage taxes and none were implemented within a sovereign Tribal nation. This study assessed the accuracy of HDNA tax implementation among 47 stores located on the Navajo Nation. A pair of tax-exempt items [e.g. a bottle of water and fresh fruit] and a pair of HDNA-tax eligible items [e.g. sugary beverage and candy bar] were purchased between July-December 2019. Receipts were retained to assess taxation. A total of 87.2% of stores accurately implemented the 2% tax on unhealthy items while 55.3% of the stores accurately implemented the 6% tax waiver on healthy items. In all, 51.1% of the stores accurately applied both taxes. There were no significant differences across store type (convenience or grocery stores and trading posts) or geographic region. In conclusion, almost all stores on the Navajo Nation accurately applied a 2% tax on unhealthy foods and beverages, while the proportion of stores applying a waiver on healthy foods was lower. Successful HDNA tax implementation among stores remains an important priority in achieving the goal to support health promotion and disease prevention among Navajo communities.