In lieu of real property taxes, special benefit assessments and sewerage system use charges otherwise payable to a municipality, a local authority shall pay each year, to the municipality in which any of its housing projects for elderly persons is located, a sum to be determined by the municipality with the approval of the Commissioner of Housing not in excess of ten per cent of the shelter rent per annum for each occupied dwelling unit in any such housing project; except that the amount of such payment shall not be so limited in any case where funds are made available for such payment by an agency or department of the United States government, but no payment shall exceed the amount of taxes which would be paid on the property were the property not exempt from taxation.