JSFiddle - React, Tailwind, and code Playground

HTML

<script src="https://cdnjs.cloudflare.com/ajax/libs/knockout/3.2.0/knockout-min.js"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/knockout-validation/2.0.2/knockout.validation.min.js"></script>
<label>Quantity: <input name="quantity" type="number" data-bind="textInput: quantity"/></label>
<label>Euros: <input name="wholeNumber" type="number" data-bind="textInput: wholeNumber"/></label>

CSS

label {
    display: block;
    margin: 10px 0;
}

JavaScript

function ViewModel() {
    self = this;
    cents = ko.observable();
    quantity = ko.observable();
    wholeNumber = ko.computed({
        read: function() {
            return (self.cents() / 100).toFixed(2); 
        },
        write: function(value) {
            self.cents(Math.round(value * 100));
            cons
        }
    });
}

ko.applyBindings(ViewModel);