JSFiddle - React, Tailwind, and code Playground

HTML

<input type="text" id="input" maxlength="14" value="" />

JavaScript

document.querySelector('#input').onchange = function () {
    if (this.value.indexOf('.') == -1) this.value += '.000';
    if (this.value.substring(this.value.indexOf('.') + 1).length < 3)
        while (this.value.substring(this.value.indexOf('.') + 1).length < 3)
    this.value += '0';
};