This could be due to a rounding issue. WooCommerce calculates taxes and discounts based on line items and then rounds at the line level, not the unit level. This is done to prevent rounding errors from accumulating.
Please navigate to tax settings, disable the “Rounding” option, and see whether it resolves or not.
I understand your concern about the rounding issue. While WooCommerce’s default tax calculation is designed to prevent rounding errors, I understand you wish to have rounding at the subtotal level.
However, you can try increasing the number of decimals to 3 and see whether it resolves your issue or not.
If it doesn’t work as expected, then you may consider using a custom function or plugin to adjust the tax calculation settings to suit your needs. However, please note that this may require some custom coding, which is beyond the scope of our support.
If you’re not comfortable with code, you might consider hiring a developer to help with this task. We recommend checking out Codeable.io, where you can hire a developer with WooCommerce expertise. You may also try these resources, which I found via Google Search: