The Expressions Cheat Sheet

The trick to achieve the South-Park animation style is to divide a number, round it and then multiply it back the same amount.
This behaves like snapping something to a grid. If we divide and multiply by 20, the spacing between the grid cells will be 20 pixels.

Snapping Position (or other 2 dimensional properties)

// properties you can edit
var stepSize = 20; // Will stick to 20 pixels incremenets

// run
var x = Math.round(value[0] / stepSize) * stepSize;
var y = Math.round(value[1] / stepSize) * stepSize;
[x, y];

Snapping Rotation (or other 1 dimensional properties)

// properties you can edit
var stepSize = 20;

// run
var result = Math.round(value / stepSize) * stepSize;

Bonus: Creating a snap function that can be applied to both kinds of properties

function snap(theValue, theStepSize) {
	if (Array.isArray(theValue)) {
		// if the value is an array (like a Position value) apply to each dimension
		var result = [];
		for (var i=0; i<theValue.length; i++) {
				result.push(Math.round(theValue[i] / theStepSize) * theStepSize);
		return result
	// otherwise, apply to the value
	return Math.round(theValue / theStepSize) * theStepSize;

snap(value, 20);

In this example we created a function that snaps a value to a specific increment just like before.
Additionaly, we can use the power of JavaScript to automatically check if the value given to the function is an array, and if it is to snap each value independently and return the result as an array as well.