Hwalker, I'm not familiar with the needs of rounding off rebar lengths, but what you describe (accurate rounding) is much more easily doable using dimensions than formula fields.
The block you posted does not seem to do what you suggest, though. The actual value of A and E is 248. The actual length of B and D is 146. The actual value of C is 246. The actual value of A+E+B+D+C=248+248+146+146+246 = 1034. IF rounded to the nearest 25mm, that would equal 1025, not the 975 your field block displays.
My last block also had an error in calculation due to the way it was set up, but I had all rounding to the nearest 5mm.
Here is a version that rounds each to value to the nearest 5mm and the overall length to the nearest 25mm.