Here is a huge problem with OpenCart...
OC can't update currencies for a while, plus it never have a real auto update function for it.
Currencies updated only when you logged into admin dashboard.
Now you have to update them with your bare hand... (I know I know, mouse and keyboard...)
That is sad, really really sad...

Well I made this extension for myself but may you can use it too.

It is a little modification what cure this flaw.
Foreign exchange rates published by the European Central Bank.

AUTO UPDATE CURRENCIES

If you turn on the auto update currencies option in settings then your currencies will be updated after you logged in into admin dashboard like in old times.

This extension have a cron file: 'catalog/controller/cron/currency_update.php', you can use it for cron and you can go to a vacation, your price will be updated if you turned on auto update option in settings.

Use this url for cron job: https://yoursite.name/index.php?route=cron/currency_update
(Of course you have to change "yoursite.name" to your site name whatever it is.)

Auto update will run only once / day avoid API overuse, but you can start force update with:
Admin > System > Localization > Currencies > Orange refresh currency values button.

INSTALLATION INSTRUCTIONS - OCMOD (ZIP)

- In "Extensions > Extension Installer" press the blue "Upload" button and upload the file "currency_update_fix_oc2x.ocmod.zip".
- In "Extensions > Modifications" press the top right blue "Refresh" button (circular arrows) to refresh the modification cache.

- Done!

If you have problems or you need support then use the contact form.