Correct way to get net/gross price and tax amount

[sandomatyas]

I'm writing a payment plugin and I want to post some information to an external server.
I wondering what is the correct way to get

• Net price of item? Maybe $order array's product_item_price? product_discountedPriceWithoutTax? product_priceWithoutTax?
• Percentage of tax? $cart->products[$id]->product_tax_id is zero but the tax amount isn't

Can you help me guys? Thanks