(b) If the ordinance calling the election on the issuance of bonds provides that all or any portion of the retail transaction and use tax authorized under Article 10 (commencing with Section 103350) be levied and used to the extent required to pay principal of and interest on the bonds, the board, in order to provide for any sinking fund payments required therefor and to create or maintain any reserve fund required therefor, shall estimate the revenues of the district which are expected to be available for such purposes and the amount to be raised by such a tax as is required to be levied and used for such purposes in order to provide for the payment of all such obligations when due. The board may, in its regular annual budget, or in a special budget which may be prepared at any time, show the amounts needed for such purposes, estimate the revenue available therefor, and thereafter fix the rates of and levy and collect, or provide for the collection of, such a tax as will provide, together with other revenues available therefor, at least all sums necessary for such purposes insofar as such levies do not exceed the maximum rates of such a tax stated in the ordinance calling the bond election. If from any cause the revenues of the district are, or are expected to be, inadequate to pay the principal of and interest on the bonds and sinking fund payments as they become due, and establish or maintain any reserve fund required therefor, and if the proceeds of such tax levied at the maximum rates authorized, together with such revenues, are still estimated to be insufficient for such purposes, the board shall levy and collect upon all property in the district taxable for county purposes a tax at least sufficient, with the revenues already collected and available therefor, together with the anticipated proceeds of the special tax, to pay the interest on the bonds that will become due and such part of the principal thereof, including any sinking fund payments, that will become due before the proceeds of a tax levied at the time of the next general tax levy will be available for such purposes, and sufficient to provide or to restore such reserve fund to the amount required by any of the district's agreements with its bondholders.