This is not supported in power store, you would need to manually edit the code for every page that displays a price to change the number format.
for example, the featured product on the index page is generated in the webassist/plugins/catalog/featuredbox.php file using this code:
<?php echo(($row_FeaturedRS)?(number_format($row_FeaturedRS['ProductPrice'],2)):"24.99"); ?>
you would need to edit the number format to 0:
<?php echo(($row_FeaturedRS)?(number_format($row_FeaturedRS['ProductPrice'],0)):"24"); ?>
there are to many other places where a price is displayed to list them all for you.