My rep graph shows numbers like 998 and 451. This annoys me so much - 998 is 2 off of 1000 / 1k and it isn't even clear what line the 998 refers to (the top of the grey segment or the bottom?).
My suggestion: Round to 1/100th of the rounded up number to 1sf:
Mine is 1,546. That rounds up to 2,000, and 1/100th is 20. Closest 20 is a reasonable number to round to.
Someone with 113,689 reputation would round to 100,000, and 1/100th is 1,000. So it would use steps of 1000.
Note that this is only the new graph in the new profile. The rep-tab graph is fine: