You may be overlooking the potential for someone to own more than one of those $100T bills. Apparently it was worth about 30 USD at the time.
If $100T = 30 USD, then probably nobody will mind if we round to the nearest $1B. Just like how I have no way to compensate someone for less than 0.01 USD.
The government cares, the precision necessary for taxes is sub cent as mentioned in some replies to the top comment on this post.