Step 1: First you need to add di.xml in the following path:

app/code/Magemonkey/PriceAdjustment/etc/frontend

Now add the below code:

<?xml version="1.0"?>
<config xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="urn:magento:framework:ObjectManager/etc/config.xsd">
    <preference for="MagentoTaxObserverUpdateProductOptionsObserver" type="MagemonkeyPriceAdjustmentObserverUpdateProductOptionsObserver" />
</config>

Step 2: Next, you need to add module.xml file in the following path:

app/code/Magemonkey/PriceAdjustment/etc

Add the below code:

<?xml version="1.0"?>
<config xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="../../../../../lib/internal/Magento/Framework/Module/etc/module.xsd">
    <module name="Magemonkey_PriceAdjustment" setup_version="1.0.0">
        <sequence>
            <module name="Magento_Tax"/>
        </sequence>
    </module>
</config>

Step 3: Now you need to add registration.php file in the following path:

app/code/Magemonkey/PriceAdjustment

Add the below code:

<?php
MagentoFrameworkComponentComponentRegistrar::register(
    MagentoFrameworkComponentComponentRegistrar::MODULE,
    'Magemonkey_PriceAdjustment',
    __DIR__
);

Step 4: Lastly, you need to add the UpdateProductOptionsObserver.php file in the following path:

app/code/Magemonkey/PriceAdjustment/Observer

And add the below code:

<?php
namespace MagemonkeyPriceAdjustmentObserver;

use MagentoFrameworkEventObserverInterface;

class UpdateProductOptionsObserver extends MagentoTaxObserverUpdateProductOptionsObserver
{
    /**
     * Tax data
     *
     * @var MagentoTaxHelperData
     */
    protected $taxData;

    /**
     * @var MagentoFrameworkRegistry
     */
    protected $registry;

    /**
     * @param MagentoTaxHelperData $taxData
     * @param MagentoFrameworkRegistry $registry
     */
    public function __construct(
        MagentoTaxHelperData $taxData,
        MagentoFrameworkRegistry $registry
    ) {
        $this->taxData = $taxData;
        $this->registry = $registry;
    }

    /**
     * Change default JavaScript templates for options rendering
     *
     * @param MagentoFrameworkEventObserver $observer
     * @return $this
     */
    public function execute(MagentoFrameworkEventObserver $observer)
    {
        $response = $observer->getEvent()->getResponseObject();
        $options = $response->getAdditionalOptions();

        $_product = $this->registry->registry('current_product');
        if (!$_product) {
            return $this;
        }

        $algorithm = $this->taxData->getCalculationAlgorithm();
        $options['calculationAlgorithm'] = $algorithm;
        // prepare correct template for options render
        if ($this->taxData->displayBothPrices()) {
            $options['optionTemplate'] = sprintf(
                '<%%= data.label %%>'
                . '<%% if (data.finalPrice.value) { %%>'
                . ' +<%%= data.basePrice.formatted %%> (%1$s <%%= data.finalPrice.formatted %%>)'
                . '<%% } %%>',
                __('Incl. tax:')
            );
        } elseif ($this->taxData->priceIncludesTax() && $this->taxData->displayPriceExcludingTax()) {
            $options['optionTemplate'] = sprintf(
                '<%%= data.label %%>'
                . '<%% if (data.basePrice.value) { %%>'
                . ' +<%%= data.basePrice.formatted %%>'
                . '<%% } %%>'
            );
        }

        $response->setAdditionalOptions($options);
        return $this;
    }
}