As long as it's not aerosol, you should be fine. Don't overstate the value on the declaration (you need to officially declare what you are sending), as the recipient will be charged taxes/duties based on the stated value.
You can go to the post office and pick up a pamphlet on what is allowed to be sent via the post office, or you can go online and read up. There always seems to be some exceptions, so it's better to be sure than to guess/assume. Different countries also have different regulations.
If you send via other means than the post office, the recipient will be charged a brokerage fee by the shipping company. It seems to be around $20-$30 for UPS and FedEx, even if the item is only $5.00.
I would also recommend you require a signature receipt so you can tell when the package arrived. Also, look at getting some sort of tracking. I've had some packages arrive in less than 2 weeks and others that took over 2 months. Both from the same state.