JSFiddle - React, Tailwind, and code Playground

HTML

<script src="https://unpkg.com/vue@2.6.14/dist/vue.js"></script>
<div id="app">
  USD:
  <input type="number" step="0.01" :value="usd.toFixed(2)" @change="updated_usd">
  <br>
  DOGE:
  <input type="number" step="0.001" :value="doge.toFixed(3)" @change="updated_doge">
  <br>
  The other will update on focus change. Haven't gotten this working with @input yet.
</div>

JavaScript

const USD_TO_DOGE = 7
const DOGE_TO_USD = 1/USD_TO_DOGE;

new Vue({
  el: '#app',
  
  data () {
    return {
	    usd: 1,
      doge: 7,
    }
  },
  
  methods: {
    updated_usd(event) {
        this.usd = event.target.valueAsNumber;
        this.doge = this.usd * USD_TO_DOGE;
    },
    updated_doge(event) {
        this.doge = event.target.valueAsNumber;
        this.usd = this.doge * DOGE_TO_USD;
    },
  },
});