How do I get y-axis ticks in vega-lite to be "nice" round numbers evenly spaced?

I'm using vega-lite in deneb for the first time. I've created a line with multi y-axis. On the right side y-axis, Vega is automatically assigning the data point exact values as the tick labels and intervals (see attached image). For example, for the % axis I want it to be 20%, 25%,30%... I want the ticks to be round numbers with even interval spacing between the ticks. Similar to how the left side y-axis is done. I've tried "tickCount" which doesn't work. I've pasted my code below too. Could it be a data type issue? Any help is greatly appreciated!

3 Axis Chart

I tried allowing vega to automatically assign the tick and intervals because I expected the default was to use round numbers. What happened was vega used the data table's exact values for the tick and intervals.

 `{
      "data": {"name": "dataset"},
      "encoding": {
        "x": {
          "field": "PERIOD_YEAR",
          "type": "nominal"
          }
   },
    "layer": [
    {
      "mark": {
        "type": "line"
      },
      "encoding": {
          "y":{
            "field": "QTY",
            "type": "quantitative"
        }
      }
    },
   {
      "mark": {
        "type": "line"
      },
      "encoding": {
        "y":{
          "field": "GM%_Less LC__formatted",
          "sort":"-y"
          }
        }
      },
    {
    "mark": {
    "type": "line"
    },
    "encoding": {
    "y": {
    "field": "GM $/unit_Less LC__formatted",
    "sort":"-y",
    "axis": {"offset":80}
      }
    }
    }
    ],
    "resolve": {"scale": {"y":"independent"}}
    }`

If you set the type to quantitative, you get nice tick values. You can set the domain extents to whatever you want. I'm confused as I thought you'd tried this? Is this the result you're looking for?

{
  "data": {
    "name": "dataset"
  },
  "encoding": {
    "x": {
      "field": "Year"
    }
  },
  "layer": [
    {
      "mark": {
        "type": "line"
      },
      "encoding": {
        "y": {
          "field": "Quantity",
          "type": "quantitative"
        }
      }
    },
    {
      "mark": {
        "type": "line"
      },
      "encoding": {
        "y": {
          "field": "GM %",
          "sort": "-y", "type": "quantitative", "scale":{"zero":false}
        }
      }
    },
    {
      "mark": {
        "type": "line"
      },
      "encoding": {
        "y": {
          "field": "GM $ / Unit",
          "sort": "-y", "type": "quantitative","scale":{"zero":false},
          "axis": {
            "offset": 80
          }
        }
      }
    }
  ],
  "resolve": {
    "scale": {
      "y": "independent"
    }
  }
}