protected function calculate_item_subtotals() {
		$merged_subtotal_taxes = array(); // Taxes indexed by tax rate ID for storage later.

		$adjust_non_base_location_prices = apply_filters( 'woocommerce_adjust_non_base_location_prices', true );
		$is_customer_vat_exempt          = $this->cart->get_customer()->get_is_vat_exempt();

		foreach ( $this->items as $item_key => $item ) {
			if ( $item->price_includes_tax ) {
				if ( $is_customer_vat_exempt ) {
					$item = $this->remove_item_base_taxes( $item );
				} elseif ( $adjust_non_base_location_prices ) {
					$item = $this->adjust_non_base_location_price( $item );
				}
			}

			$item->subtotal = $item->price;

			if ( $this->calculate_tax && $item->product->is_taxable() ) {
				$item->subtotal_taxes = WC_Tax::calc_tax( $item->subtotal, $item->tax_rates, $item->price_includes_tax );
				$item->subtotal_tax   = array_sum( array_map( array( $this, 'round_line_tax' ), $item->subtotal_taxes ) );

				if ( $item->price_includes_tax ) {
					// Use unrounded taxes so we can re-calculate from the orders screen accurately later.
					$item->subtotal = $item->subtotal - array_sum( $item->subtotal_taxes );
				}

				foreach ( $item->subtotal_taxes as $rate_id => $rate ) {
					if ( ! isset( $merged_subtotal_taxes[ $rate_id ] ) ) {
						$merged_subtotal_taxes[ $rate_id ] = 0;
					}
					$merged_subtotal_taxes[ $rate_id ] += $this->round_line_tax( $rate );
				}
			}

			$this->cart->cart_contents[ $item_key ]['line_tax_data']     = array( 'subtotal' => wc_remove_number_precision_deep( $item->subtotal_taxes ) );
			$this->cart->cart_contents[ $item_key ]['line_subtotal']     = wc_remove_number_precision( $item->subtotal );
			$this->cart->cart_contents[ $item_key ]['line_subtotal_tax'] = wc_remove_number_precision( $item->subtotal_tax );
		}

		$items_subtotal = $this->get_rounded_items_total( $this->get_values_for_total( 'subtotal' ) );

		$this->set_total( 'items_subtotal', round( $items_subtotal ) );
		$this->set_total( 'items_subtotal_tax', wc_round_tax_total( array_sum( $merged_subtotal_taxes ), 0 ) );

		$this->cart->set_subtotal( $this->get_total( 'items_subtotal' ) );
		$this->cart->set_subtotal_tax( $this->get_total( 'items_subtotal_tax' ) );
	}