Hello @kowsigan_atsaya ,
I think you are using some third party module because of which this issue arises. Disable all third party modules, remove the generated folder by
rm -rf generated/*
Compile the code by
bin/magento setup:di:compile
Then deploy the static content by
bin/magento setup:static-content:deploy
Flush the cache
bin/magento cache:flush
And then check again on frontend.
If the issue is resolved then you need to check which third party module affecting you order total.
I hope this will help you, if still you face the issue, let me know.
If it helps you, please accept it as solution and give kudos.
Regards.