do senior citizens have to pay taxes on the total social security received for the year?
If the only income you received during the tax year was your social security or equivalent railroad retirement benefits, your benefits are probably not taxable and you probably will not have to file a tax return.
If you also received other income, your benefits will not be taxed unless your modified adjusted gross income is more than the base amount for your filing status.
See http://www.irs.gov/taxtopics/tc423.html