Here’s a little puzzle for you, from that eternal font of delight, the Internal Revenue Manual. The Internal Revenue Manual illustrates how an issuer should present-value or future-value penalty amounts in a VCAP or in an audit:

[A] closing agreement expected to be executed on January 15, 2016 includes amounts corresponding to future tax years 2015 through 2026. The amounts representing estimated tax payments due on the assumed April 15 tax payment dates for years 2012 through 2015 would be present valued at the short-term AFR; the amounts assumed to be due on the April 15 tax payment dates for years 2019 through 2024 would be present valued at the mid-term AFR; and the amounts assumed to be due on the April 15 tax payment dates for years 2025 and 2024 would be present valued at the long-term AFR. The applicable AFRs in effect on January 15, 2016 would be the rates used in these present value computations.” (IRM 4.81.6.5.3.9 (01-28-2016)).