@dkumar,
You can fix the maximum y-value of the data set to the top most gridline of Y-axis by dynamically setting the Y-axis minimum and maximum to minimum and maximum of the data set. And In case the gridline does not align with the maximum y-value of the data points, you can make use of y-axis stripline to represent the same. Kindly refer to this JSfiddle for the working example on the same.
If you still facing issue, kindly share a sample project along with the data and brief us more about your issue so that we can understand the scenario better and help you out.
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Sachin Bisht
Team CanvasJS