Use nicely rounded tick marks when using Binary Y-axis units

Steps to reproduce:
* Switch a graph to use the "Binary" Y-Value unit prefix
* Specify some "Total Tick Marks" (e.g., 5)
* View the graph

Expected behavior:
* Tick marks use nicely rounded numbers

Actual behavior:
* Tick marks use particular numbers with many significant digits.

Environment info:
* System info: Linux 4.15.0-163-generic
* InfluxDB version: InfluxDB 2.1.1
* Other relevant environment details: n/a

This uses tick marks like 1.1411, 3.3164, 5.4918, 7.6671, and 9.8424 instead of nice round number like 1, 3, 5, 7, and 9.

Reproduce the graph with the Binary Y-Value unit prefix and a specified Total Tick Marks value such as 5, using the issue's example as the reference. Trace the tick-mark calculation from the graph view and verify that the displayed values use rounded numbers rather than values with many significant digits.

Written by the indexing model from the issue text.