chart.js 2.1

HTML

<script src="https://cdnjs.cloudflare.com/ajax/libs/Chart.js/2.1.0/Chart.bundle.min.js"></script>
<canvas id="myChart"></canvas>

JavaScript

// round corners
	        // round corners
        Chart.pluginService.register({
            afterUpdate: function (chart) {
                if (chart.config.options.elements.arc.roundedCornersFor !== undefined) {
                    var a=chart.config.data.datasets.length -1;
                    for (let i in chart.config.data.datasets) {
                        var arc = chart.getDatasetMeta(i).data[chart.config.options.elements.arc.roundedCornersFor];
                        
                        arc.round = {
                            x: (chart.chartArea.left + chart.chartArea.right) / 2,
                            y: (chart.chartArea.top + chart.chartArea.bottom) / 2,
                            radius: chart.innerRadius + chart.radiusLength / 2 + (a * chart.radiusLength),
                            thickness: chart.radiusLength / 2 - 1,
                            backgroundColor: arc._model.backgroundColor
                        }
                        a--;
                    }
                }
            },

            afterDraw: function (chart) {
                if (chart.config.options.elements.arc.roundedCornersFor !== undefined) {
                    var ctx = chart.chart.ctx;
                    for (let i in chart.config.data.datasets) {
                        var arc = chart.getDatasetMeta(i).data[chart.config.options.elements.arc.roundedCornersFor];
                        var startAngle = Math.PI / 2 - arc._view.startAngle;
                        var endAngle = Math.PI / 2 - arc._view.endAngle;

                        ctx.save();
                        ctx.translate(arc.round.x, arc.round.y);
                        console.log(arc.round.startAngle)
                        ctx.fillStyle = arc.round.backgroundColor;
                        ctx.beginPath();
                        ctx.arc(arc.round.radius * Math.sin(startAngle), arc.round.radius * Math.cos(startAngle), arc.round.thickness, 0, 2 * Math.PI);
                      ...