Yes, some American retailers will ship to Nicaragua.
I always tend to buy stuff online. I really like online shopping, and yes, most of the stores offer the shipping to Nicaragua, for an international delivery fee, which when you think about it, is not really that much.
Some of the stores even change the currency to cordobas (Nicaragua's currency) to make it easier to shop. In case you don't need this you can just switch it back to dollars and have it that way.
If some of the stores do not offer the option to ship to Nicaragua, that would not be an issue.
NICABOX is a company which provides you with a mailbox with an U.S address. How does it work you may ask?
All you have to do is pay an annual fee of $30, and they provide you with a US address where you have others ship to you. Then NICABOX handles all of the customs issues, and you'll only have to pay the fee requested by the customs office.