Prior to display, prices are processed through a central price handler system that gives modules the chance to adjust the price value and the way it the price is formatted for display. This enables core and contributed modules to perform operations like currency conversion, product discounts, or altering product prices to include tax. To do these things, modules define price alterers and formatters that are configurable through the price handler settings page:
Price alterers may change the numeric value of a price prior to display (i.e. converting it to units of another currency) as well as the options that will be passed to the price formatter (i.e. specifying a different currency sign). All available alterers are listed in a table at the top of the page. When a price is being prepared for display, it will be processed through any enabled alterers in their order in the table. Different modules aren't necessarily aware of each other, so you may need to manually readjust your alterers for them to work together properly. You can reorder them by dragging the rows and disable them by unchecking the appropriate Enabled checkbox.
Price formatters add all of the pieces around the numeric price value so it looks like an price when displayed and not just a number on the page. Whereas any number of price alterers may be used, only one price formatter is used to display the price. If a module you enable offers another price formatter, you must select it in the list of radio buttons here to begin using it for display.
Processing prices for display can get complex, especially on sites that use multiple price alterers. As such, the price handler will temporarily cache prices by default for a slight performance gain. If you're testing or developing a new alterer, you should disable the cache by unchecking the checkbox until you've reached the performance you're expecting. Be sure to turn it back on when you're finished.