The general consensus seems to be creating multiple offers, one for each currency.
Source:
https://support.google.com/webmasters/thread/80739992?hl=en
https://moz.com/community/q/international-seo-ecommerce-rich-snippets#reply_292857
Example:
<div itemtype="http://schema.org/Product" itemscope>
<meta itemprop="name" content="Google Nexus 7">
<meta itemprop="sku" content="abc123">
<meta itemprop="gtin14" content="00886227537143" />
<div itemprop="offers" itemscope itemtype="http://schema.org/Offer">
<meta itemprop="price" content="229.95" />
<meta itemprop="priceCurrency" content="USD" />
</div>
<div itemprop="offers" itemscope itemtype="http://schema.org/Offer">
<meta itemprop="price" content="27800" />
<meta itemprop="priceCurrency" content="JPY" />
</div>
</div>
Other references:
https://schema.org/Offer