You can calculate the max of your data, and set the max of the chart based on that value, or 5, whichever is higher:
var max = 5;
for (var i = 1; i < data.getNumberOfColumns(); i++) {
if (data.getColumnType(i) == 'number') {
var range = data.getColumnRange(i);
max = Math.max(max, range.max);
}
}
Then in the chart's options, set max: max
.