When selecting the "Inclusive" tax type, it adds the tax on top of the items subtotal price which results in a total due of $12 (instead of $10).
When selecting the "Exclusive" tax type, it shows the actual Inclusive total due (also on Step 4) of $10 (instead of $12) but the Invoice generated in background and payment amount parsed to the gateway e.g. PayPal is $12.
BUG: Inclusive and Exclusive tax amount is incorrect calculated and generated Invoices are different from the amount displayed during the checkout process.
This was tested with the Standard, Ajax and Wizard order form.
The error appeared on all of them. It's either overcharging the customer, lowering the price to match the desired total price or not charge tax at all.
If this is a confirmed bug, the severity is CRITICAL and needs immediate attention.