bar chart axis issue

I have made a bar char which have two columns per category. These columns can have positive or negative values. The y-axis values does not seem to be consistent even after setting the number of y-axis values tick. I am quite curious on how that property is being computed

What about something like this:

 "signals": [
    {"name": "a", "update": "pluck(data('parsed'), 'max')"},
    {"name": "b", "update": "length(split(toString(a),'.')[0])"},
    {
      "name": "c",
      "update": "ceil(a/toNumber(pad('1',b,'0')))*toNumber(pad('1',b,'0'))"
    }
  ],


 "domainMax": {"signal": "c"}