If the value is a text type:

parseFloat("123.456").toFixed(2);

If the value is a number:

var numb = 123.23454;
numb = numb.toFixed(2);

There is a downside that values like 1.5 will give "1.50" as the output. A fix suggested by @minitech:

var numb = 1.5;
numb = +numb.toFixed(2);
// Note the plus sign that drops any "extra" zeroes at the end.
// It changes the result (which is a string) into a number again (think "0 + foo"),
// which means that it uses only as many digits as necessary.

It seems like Math.round is a better solution. But it is not! In some cases it will not round correctly:

Math.round(1.005 * 100)/100 // Returns 1 instead of expected 1.01!

toFixed() will also not round correctly in some cases (tested in Chrome v.55.0.2883.87)!

Examples:

parseFloat("1.555").toFixed(2); // Returns 1.55 instead of 1.56.
parseFloat("1.5550").toFixed(2); // Returns 1.55 instead of 1.56.
// However, it will return correct result if you round 1.5551.
parseFloat("1.5551").toFixed(2); // Returns 1.56 as expected.

1.3555.toFixed(3) // Returns 1.355 instead of expected 1.356.
// However, it will return correct result if you round 1.35551.
1.35551.toFixed(2); // Returns 1.36 as expected.

I guess, this is because 1.555 is actually something like float 1.55499994 behind the scenes.

Solution 1 is to use a script with required rounding algorithm, for example:

function roundNumber(num, scale) {
  if(!("" + num).includes("e")) {
    return +(Math.round(num + "e+" + scale)  + "e-" + scale);
  } else {
    var arr = ("" + num).split("e");
    var sig = ""
    if(+arr[1] + scale > 0) {
      sig = "+";
    }
    return +(Math.round(+arr[0] + "e" + sig + (+arr[1] + scale)) + "e-" + scale);
  }
}

It is also at Plunker.

Note: This is not a universal solution for everyone. There are several different rounding algorithms. Your implementation can be different, and it depends on your requirements. See also Rounding.

Solution 2 is to avoid front end calculations and pull rounded values from the backend server.

Another possible solution, which is not a bulletproof either.

Math.round((num + Number.EPSILON) * 100) / 100

In some cases, when you round a number like 1.3549999999999998, it will return an incorrect result. It should be 1.35, but the result is 1.36.

var number = 123.456;

console.log(number.toFixed(1)); // should round to 123.5