(1) In making an apportionment, allowances shall be made for any exemptions granted, any classification made of persons interested in the estate and for any deductions and credits allowed by the law imposing the tax.

(2) Any exemption or deduction allowed by reason of the relationship of any person to the decedent or by reason of the purposes of the gift inures to the benefit of the person bearing that relationship or receiving the gift. When an interest is subject to a prior present interest which is not allowable as a deduction the tax apportionable against the present interest shall be paid from principal.

(3) Any deduction for property previously taxed and any credit for gift taxes or death taxes of a foreign country paid by the decedent or his estate inures to the proportionate benefit of all persons liable to apportionment.

(4) Any credit for inheritance, succession or estate taxes or taxes in the nature thereof in respect to property or interests includable in the estate inures to the benefit of the persons or interests chargeable with the payment thereof to the extent that, or in proportion as the credit reduces the tax.

(5) To the extent that property passing to or in trust for a surviving spouse or any charitable, public, or similar gift or bequest does not constitute an allowable deduction for purposes of the tax solely by reason of an inheritance tax or other death tax imposed upon and deductible from the property, the property shall not be included in the computation provided for in this chapter and to that extent no apportionment shall be made against the property. This does not apply in any instance where the result will be to deprive the estate of a deduction otherwise allowable under Section 2053(d) of the Internal Revenue Code of 1986, as amended, of the United States, relating to deduction for state death taxes on transfers for public, charitable, or religious uses.