Add multi-currency support to online store (auto currency by location)

Looking for a developer to add multi-currency support to an existing online store. Right now prices are shown in a single currency only, but many visitors come from other countries and expect to see prices in a currency they actually use — dollars, euros, hryvnia. The store should detect the visitor's currency automatically by location, while still letting shoppers switch it manually from a selector in the header.

The exchange rate must come from a live, reliable source and refresh on a schedule, not be hardcoded. Just as important is the math: rounding, minor units, conversion fees, and the final charged amount must match exactly what gets billed to the card. Even a small mismatch damages trust and leads to disputes and refunds.

The currency shown also needs to stay consistent everywhere a price appears — confirmation emails, account area, order history — so a buyer never sees one currency at checkout and a different one later.

What the finished work should include:
— automatic currency detection by location, with a manual override that persists;
— integration with a live exchange-rate source and scheduled updates;
— accurate recalculation of price, fees and total in the selected currency;
— consistent display across storefront, account area, emails and history;
— testing across several currencies before handoff.