I think the calculation is made based on a comparison with the full walk-on fare with the 0.66 railcard multiplier (giving £29.96, thus a saving of £12.81) but before rounding (which gives the correct fare of £29.95, a saving of £12.80).
I don't know how the fares database works in any detail but maybe it just makes the calculation a bit simpler for cases like this where it's not critical to get the number exactly right.
edit: I had assumed you were wondering how you get a fare ending in 96p, since all fares should be multiples of 5p. If you're just asking what the fare is, it's just an Off Peak Return (SVR) which is £29.95 with Railcard discount. Valid on any Virgin service with no time restrictions (the easement mentioned by SS4).
Cheaper still are the London Midland Only fares: Off Peak Return is £18.50, Super Off Peak Return is £13.85. Chiltern offer Via High Wycombe fares as well - obviously these require a change and are more expensive than the LM Only fares.