myChart.js

function float2dollar(value){
    return "U$ "+(value).toFixed(2).replace(/\d(?=(\d{3})+\.)/g, '$&,');
}

function renderChart(data, labels) {
    var ctx = document.getElementById("myChart").getContext('2d');
    var myChart = new Chart(ctx, {
        type: 'line',
        data: {
            labels: labels,
            datasets: [{
                label: 'This week',
                data: data,
                borderColor: 'rgba(75, 192, 192, 1)',
                backgroundColor: 'rgba(75, 192, 192, 0.2)',
            }]
        },
        options: {            
            scales: {
                yAxes: [{
                    ticks: {
                        beginAtZero: true,
                        callback: function(value, index, values) {
                            return float2dollar(value);
                        }
                    }
                }]                
            }
        },
    });
}