31 C.F.R. § 359.55
How are redemption values calculated for book-entry Series I savings bonds?
We base current redemption values (CRV) for book-entry Series I savings bonds on the definitive savings bonds CRV. To calculate the book-entry values, we use the CRV for the $100 denomination Series I savings bonds and calculate a CRV prorated to the book-entry par investment amount for the corresponding issue and redemption dates. Calculated book-entry CRV will be rounded to the nearest one cent.