Read this: Individual states and localities offer nonprofits exemptions from other taxes such as sales tax or property tax. Federal tax-exempt status does not guarantee exemption from state and local taxes, and vice versa. These exemptions generally have separate applications and their requirements may differ from the IRS requirements. Furthermore, even a tax exempt organization may be required to file annual financial reports (IRS Form 990) at the state and federal level. A tax exempt organization's 990 forms are required to be made available for public scrutiny. An example of nonprofit organization in the US is Project Vote Smart.
Now answer this question, if there is an answer (If it cannot be answered, return "unanswerable"): What form must an NPO make available to the public?
990 forms