I'll share additional details about changing a home currency within the program, Janna.

You don't need to register a QuickBooks for the USA region to have a USD home currency because you can set it up in a QuickBooks Online (QBO) South Africa account. Simply enable the multicurrency feature, then change the home currency to USD. 

However, if you still want to use QuickBooks US instead, visit this link for the plans and pricing: https://quickbooks.intuit.com/pricing/.

 You'll want to learn how to track the changes in exchange rates on foreign balances within the program. Check out this article: Enter home currency adjustments for your foreign balances.

Let me know if you require any further clarification about QuickBooks currency. I'll get back to you quickly.