(1) All bonds or other evidences of debt having a fixed term and rate of interest held by an insurer, if secured and not in default as to principal or interest, may be valued as follows:
(a) If purchased at par, at the par value.
(b) If purchased above or below par, on the basis of the purchase price adjusted to bring the value to par at maturity and to yield in the meantime the effective rate of interest at which the purchase was made, or in lieu of this method, according to any accepted method of valuation approved by the Department of Insurance.
(c) Purchase price shall not be taken at a higher figure than the actual market value at the time of purchase, plus actual brokerage, transfer, postage or express charges paid in the acquisition of the securities.
(2) The Department of Insurance shall have full discretion in determining the method of calculating values according to the rules set forth in this section, but no method or valuation shall be inconsistent with any applicable valuation or method used by insurers in general or any method formulated or approved by the National Association of Insurance Commissioners or its successor organization.