Tax Calculation Issue

[angelleye]

We have a user reporting a problem with tax calculations: https://wordpress.org/support/topic/paypal-tax-total-is-invalid-error?replies=3#post-8665919

I know we've done quite a bit of calculation / adjustment in the past trying to resolve issues with cart items not adding up to the subtotal getting sent to PayPal, and we had logic where we would adjust shipping or tax based on what was available to adjust.

I think our calculation is causing the tax to be negative in this case. The user provided details about how their site is configured so we can try to reproduce.