Qualified Nonprofit organizations are exempted from paying taxes. If a NPO starts doing activities that aren't related to their basic purpose, then they have to pay taxes.

http://www.investopedia.com/ask/answers/08/nonprofit-tax.asp

why do we have non profit organizations

No, not all nonprofit Organizations are reputable, you must search for their history and judge on your own.

Nonprofit organizations who own property (real or personal) are responsible for property taxes unless they qualify for tax exempt status. Nonprofit organizations are not automatically assumed to have met the qualifications for tax exemption status in most states and must file information with local taxing authorities, who then determine their taxable status. Qualifying for nonprofit status under IRS section 501 (c)(3) does not automatically mean the organization qualifies for property tax exempt status in many states. In some states the nonprofit organization must own and occupy the property for which the exemption is sought (they can't use it for another purpose or lease it to others).

The best bet is to contact local nonprofit organizations. You can then have them write you a letter and you can write the donation off on your taxes.