The edges appear to be slightly slanted inward, and there is some strike doubling on the bottom of the image of Monticello. This seems to appear on coins from the late 60s/early 70s to the mid-late 90s.
The nickel went through a number of design changes at the end of the time period you referenced. How the obverse and reverse dies form the shape of the rim may have altered a bit too though I have not noted it. One thing that has not changed is that the collar, which forms the edge, is perpendicular to the other die faces . The edge of a coin , since a collar was first used in the 1800's , will be at 90 degrees from the coin face.
From the rim to the center of the lettering is slanted slightly isn't it? In addition, the picture of Monticello seems to be underlined. The edge of the slanted area is marked with a black circle and doubling of the bottom of Monticello is marked with black lines. The edge of the slant is most visible directly under E PLURIBUS UNUM. The doubling is faint, and is more visible if you view it at an angle from the bottom of the coin. It seems to be on most nickels from that time. The edge issue does not appear to be with the collar so much as the edges of the dies.
That seems reasonable. The nickles from that time period seem to have been upset in such a way that the edges of the striking surface are slightly raised, so that the coin is shaped like: |\____________/| |/------------\| instead of: |--------------| |--------------| which could be caused by a different way of upsetting the rims.
