angularjs input保留两位小数 (type 不是number)?

Question

<input type="text" ng-model="vm.price" name="price" placeholder="请输入成交单价" required/>
<input type="text" ng-model="vm.number" name="number" placeholder="请输入成交数量" required/>
<input type="text" ng-model="vm.amount" name="amount" placeholder="请输入成交价格" required/>

vm.amount = vm.price * vm.number 怎么保留两位小数?

希望得到大家的帮助,谢谢!