What's the point of NCR currency?
To use as a substitute for toilet paper.
That be expensive toilet paper, a single $5 note is still worth two caps. Pre-war money on the other hand comes in stacks of about one hundred for $10 caps, adjusted for barter. Much better deal.
*The iconic wad of cash you see in the film, is one hundred bills bundled together, thus I assume a stack of pre-war money is the same way.