BUG: Fix dt64[non_nano] + offset rounding

Author: Aniketsy

pandas/core/arrays/datetimes.py

@@ -827,22 +827,17 @@ def _add_offset(self, offset: BaseOffset) -> Self:
             if hasattr(offset, "offset"):
                 offset_td = Timedelta(offset.offset)
                 offset_unit = offset_td.unit
-                if self.unit in units and offset_unit in units:
-                    idx_self = units.index(self.unit)
-                    idx_offset = units.index(offset_unit)
-                    res_unit = units[min(idx_self, idx_offset)]
+                idx_self = units.index(self.unit)
+                idx_offset = units.index(offset_unit)
+                res_unit = units[min(idx_self, idx_offset)]
             result = type(self)._simple_new(res_values, dtype=res_values.dtype)
             result = result.as_unit(res_unit)
 
             if offset.normalize:
                 result = result.normalize()
                 result._freq = None
 
-            if (
-                self.tz is not None
-                and getattr(result.dtype, "tz", None) is None
-                and res_unit == "ns"
-            ):
+            if self.tz is not None:
                 result = result.tz_localize(self.tz)
 
         return result