Fixes rounding issues around tax and floats

- tax amounts are truncated to 6 decimals before being added to totals
- same for discounts
- fixes #147

Signed-off-by: Christopher Rogers <[email protected]>

lib/recurly/pricing/calculations.js

@@ -94,8 +94,8 @@ Calculations.prototype.tax = function (done) {
       } else {
         each(taxes, function (tax) {
           if (tax.type === 'usst' && self.items.plan.tax_exempt) return;
-          self.price.now.tax += self.price.now.subtotal * tax.rate;
-          self.price.next.tax += self.price.next.subtotal * tax.rate;
+          self.price.now.tax += parseFloat((self.price.now.subtotal * tax.rate).toFixed(6));
+          self.price.next.tax += parseFloat((self.price.next.subtotal * tax.rate).toFixed(6));
         });
 
         // tax estimation prefers partial cents to always round up
@@ -156,8 +156,10 @@ Calculations.prototype.discount = function () {
 
   if (coupon) {
     if (coupon.discount.rate) {
-      this.price.now.discount = Math.round(this.price.now.subtotal * coupon.discount.rate * 100) / 100;
-      this.price.next.discount = Math.round(this.price.next.subtotal * coupon.discount.rate * 100) / 100;
+      var discountNow = parseFloat((this.price.now.subtotal * coupon.discount.rate).toFixed(6));
+      var discountNext = parseFloat((this.price.next.subtotal * coupon.discount.rate).toFixed(6));
+      this.price.now.discount = Math.round(discountNow * 100) / 100;
+      this.price.next.discount = Math.round(discountNext * 100) / 100;
     } else {
       this.price.now.discount = coupon.discount.amount[this.items.currency];
       this.price.next.discount = coupon.discount.amount[this.items.currency];