JSFiddle - React, Tailwind, and code Playground

HTML

<input type="text" name="network_top_cashback" id="network_top_cashback" value="" size="4" class="inputt" />
<br>
<input type="text" name="cashback_coef" id="cashback_coef" value="" size="4" class="inputt" />
<br>
<input type="text" readonly="readonly" name="member_top_cashback" id="member_top_cashback" value="" size="4" class="inputt" />

JavaScript

$(document).ready(function () { 
        $("#network_top_cashback, #cashback_coef").change(function() {
$("#member_top_cashback").val($("#network_top_cashback").val() * $("#cashback_coef").val());

var num =$("#member_top_cashback").val();
num = num.toFixed(2);
        });
    });

$( function() {
 $('#network_top_cashback').keyup(function(){
   if($(this).val().indexOf('.')!=-1){         
       if($(this).val().split(".")[1].length > 2){                
           if( isNaN( parseFloat( this.value ) ) ) return;
           this.value = parseFloat(this.value).toFixed(2);
       }  
    }            
    return this;
 });
});

$( function() {
 $('#cashback_coef').keyup(function(){
   if($(this).val().indexOf('.')!=-1){         
       if($(this).val().split(".")[1].length > 5){                
           if( isNaN( parseFloat( this.value ) ) ) return;
           this.value = parseFloat(this.value).toFixed(2);
       }  
    }            
    return this;
 });
});

$('input#member_top_cashback').blur(function(){
    var num = parseFloat($(this).val());
    var cleanNum = num.toFixed(2);
    $(this).val(cleanNum);
    
    });