Commercial invoice shows goods sold, unit cost and quantity. Typically, it will be in US dollars but it can also be written in a local currency.
There are two things you need to watch out for. Watch out for mistakes in extensions and watch out for discrepancy against the packing list! The fact that the invoice and the packing list may not match will be enough for the US Customs to ask your broker for the shipment to be moved to an inspection site where the customs officials then perform “shipment inspection” — they look at the goods to assure themselves whether the discrepancy is but a typing error between the commercial invoice and the packing list or an outright violation intended perhaps to lower the goods’ total dutiable amount. Not only that they will find the error in count, they may also reclassify the goods if they think that the goods were entered under a wrong category out of the Harmonized Tariff Schedule, especially if higher duty rate will apply. One way or another, even if they find no problem with the goods, the move to an exam site will always constitute an additional expense for the inspection itself, adding to your landed cost of your imported goods, not to mention a delay, and often can also result in potential damages to your goods that may occur during the inspection.