Revert change 0eb8c182131e:

"""Issue #23517: datetime.timedelta constructor now rounds microseconds to
nearest with ties going away from zero (ROUND_HALF_UP), as Python 2 and Python
older than 3.3, instead of rounding to nearest with ties going to nearest even
integer (ROUND_HALF_EVEN)."""

datetime.timedelta uses rounding mode ROUND_HALF_EVEN again.

Modules/_datetimemodule.c

@@ -2149,9 +2149,29 @@ delta_new(PyTypeObject *type, PyObject *args, PyObject *kw)
     if (leftover_us) {
         /* Round to nearest whole # of us, and add into x. */
         double whole_us = round(leftover_us);
+        int x_is_odd;
         PyObject *temp;
 
-        whole_us = _PyTime_RoundHalfUp(leftover_us);
+        whole_us = round(leftover_us);
+        if (fabs(whole_us - leftover_us) == 0.5) {
+            /* We're exactly halfway between two integers.  In order
+             * to do round-half-to-even, we must determine whether x
+             * is odd. Note that x is odd when it's last bit is 1. The
+             * code below uses bitwise and operation to check the last
+             * bit. */
+            temp = PyNumber_And(x, one);  /* temp <- x & 1 */
+            if (temp == NULL) {
+                Py_DECREF(x);
+                goto Done;
+            }
+            x_is_odd = PyObject_IsTrue(temp);
+            Py_DECREF(temp);
+            if (x_is_odd == -1) {
+                Py_DECREF(x);
+                goto Done;
+            }
+            whole_us = 2.0 * round((leftover_us + x_is_odd) * 0.5) - x_is_odd;
+        }
 
         temp = PyLong_FromLong((long)whole_us);