Move internal modules to “internal” folder.

.internal/createRound.js

@@ -0,0 +1,33 @@
+import toInteger from './toInteger.js';
+import toNumber from './toNumber.js';
+import toString from './toString.js';
+
+/* Built-in method references for those with the same name as other `lodash` methods. */
+const nativeMin = Math.min;
+
+/**
+ * Creates a function like `round`.
+ *
+ * @private
+ * @param {string} methodName The name of the `Math` method to use when rounding.
+ * @returns {Function} Returns the new round function.
+ */
+function createRound(methodName) {
+  const func = Math[methodName];
+  return (number, precision) => {
+    number = toNumber(number);
+    precision = precision == null ? 0 : nativeMin(toInteger(precision), 292);
+    if (precision) {
+      // Shift with exponential notation to avoid floating-point issues.
+      // See [MDN](https://mdn.io/round#Examples) for more details.
+      let pair = `${ toString(number) }e`.split('e');
+      const value = func(`${ pair[0] }e${ +pair[1] + precision }`);
+
+      pair = `${ toString(value) }e`.split('e');
+      return +`${ pair[0] }e${ +pair[1] - precision }`;
+    }
+    return func(number);
+  };
+}
+
+export default createRound;