I am looking for an app that can change the currency and that makes it so that I can change the exchange rate or can change what the currency is.
Also I need an app that can change the currency in the checkout so people can checkout in the currency that they want.
I need an app that does both of these.
Currency Converter Box probably meets your need. This app is easy to setup and automatically changes the currency adaptive to customers' location and the checkout proceess.
Hi! Shopify provides currency converter which allows multiple currencies, but it is for visual only. Customers still need to check out by default currency.
If you really want to provide multiple currencies both visual and upon check out, it's better you run multiple-sites, for example, exampleshop.com for the US market, exampleshop.com.au for Australia market, and etc. It gives you the best flexible to control differences among prices, currencies, inventory, and etc.
Among multiple-site, you could detect your visitor IP and auto redirect your visitors to correct site based on their IP geo locations, for example, use Geo Targetly - Geo Redirect tool. It's easy to set and integrate within a few steps. No code is necessary by yourself.
Hope it helps!