I have chart looking like that:
I use measure axis for Y:
y = myChart.addMeasureAxis(
I'm afraid overriding minimum axis values is a little suboptimal at the moment. There is a workaround but it's a bit of a hack. Basically you just hide the x axis entirely and draw a second chart with no series over the top, hiding the second chart's y axis.
So after drawing do:
c2 = new dimple.chart(svg, data);
c2.addCategoryAxis("x", "Day");
c2.addMeasureAxis("y", "Value").hidden = true;
c2.draw();
The two axes meet up nicely and look the way you would want.
Here is a working example:
http://jsfiddle.net/87GHM/2/