diff --git a/homeassistant/components/energy/sensor.py b/homeassistant/components/energy/sensor.py
index 387a08141a2..0c4c5eeb3b9 100644
--- a/homeassistant/components/energy/sensor.py
+++ b/homeassistant/components/energy/sensor.py
@@ -221,7 +221,6 @@ class EnergyCostSensor(SensorEntity):
         self._attr_state_class = STATE_CLASS_TOTAL
         self._config = config
         self._last_energy_sensor_state: State | None = None
-        self._cur_value = 0.0
         # add_finished is set when either of async_added_to_hass or add_to_platform_abort
         # is called
         self.add_finished = asyncio.Event()
@@ -229,7 +228,6 @@ class EnergyCostSensor(SensorEntity):
     def _reset(self, energy_state: State) -> None:
         """Reset the cost sensor."""
         self._attr_native_value = 0.0
-        self._cur_value = 0.0
         self._attr_last_reset = dt_util.utcnow()
         self._last_energy_sensor_state = energy_state
         self.async_write_ha_state()
@@ -339,8 +337,8 @@ class EnergyCostSensor(SensorEntity):
             self._reset(energy_state_copy)
         # Update with newly incurred cost
         old_energy_value = float(self._last_energy_sensor_state.state)
-        self._cur_value += (energy - old_energy_value) * energy_price
-        self._attr_native_value = round(self._cur_value, 2)
+        cur_value = cast(float, self._attr_native_value)
+        self._attr_native_value = cur_value + (energy - old_energy_value) * energy_price
 
         self._last_energy_sensor_state = energy_state