I am very new, so until someone wiser comes along, this is what I do. My scale doesn't measure in tenths. Just solid grams. When I am measuring lye, I round down, unless it is a very high tenth (.9 ish) and then I just get to the grams I need and ass a tiny bit extra, but not enough to make it go to the next tenth. I do this with my oils as well. But when in doubt, I err on the side of caution and round up for oils and down for lye.
Again, I am new, but my thinking is that with a superfat of 5 - 10%, less than a gram is not going to hurt anyone, if anything it will only ensure that I never get a recipe down perfect and the same as before. When you are dealing with hundreths of a gram, I would think that would be the case, even more so.
ETA: Sorry, I just saw you were talking about ounces and not grams. With that I don't know what I would do. I guess find out the number of grams in tenths of an ounce with google's calculator and do as I was before on grams.