Improper significant figures getting calculated

[ghansham]

Assuming a range of 477 to 945.
The values for labels get calculated as 477, 594, 711, 828, 945.
sigfigs value gets calculated as 1. which rounds off 477 to 480 and 945 to 950.

edal-java/graphics/src/main/java/uk/ac/rdg/resc/edal/graphics/style/MapImage.java

Line 466 in 1eb2a92

int sigfigs = (int) Math.ceil(Math.log10(max / minDiff));

Can something be done to calculate it correctly?