Round *special price only* in Magento - php

Question

I have a situation where the customer wants the special price to be rounded to the nearest whole number (Example: 1922.25 => 1922.00, 1256.85 => 1257.00)
This should be only for Special prices says the customer which means, if there's no special price for the product, the price should come as it is.
Note this is not only for display. This rule applies everywhere, even invoices. So is there a way to do this easily or we should only modify the core files?
EDIT
If we modify the core framework files like Product.php or Price.php, they will get overwritten with an update right? So this should be a safe way too preferably.

Answer 1

This is pretty easy.
Just observe catalog_product_load_after event, and overwrite special_price with a rounded value.
Create a bootstrap file for your module:
app/etc/modules/Danslo_RoundSpecialPrice.xml:
<?xml version="1.0" encoding="UTF-8"?>
<config>
<modules>
<Danslo_RoundSpecialPrice>
<active>true</active>
<codePool>local</codePool>
<depends>
<Mage_Catalog />
</depends>
</Danslo_RoundSpecialPrice>
</modules>
</config>
Specify that we want to observe the product load event:
app/code/local/Danslo/RoundSpecialPrice/etc/config.xml:
<?xml version="1.0" encoding="UTF-8"?>
<config>
<global>
<models>
<roundspecialprice>
<class>Danslo_RoundSpecialPrice_Model</class>
</roundspecialprice>
</models>
<events>
<catalog_product_load_after>
<observers>
<round_special_price>
<class>roundspecialprice/observer</class>
<type>singleton</type>
<method>roundSpecialPrice</method>
</round_special_price>
</observers>
</catalog_product_load_after>
<catalog_product_collection_load_after>
<observers>
<round_special_price>
<class>roundspecialprice/observer</class>
<type>singleton</type>
<method>roundSpecialPriceInCollection</method>
</round_special_price>
</observers>
</catalog_product_collection_load_after>
</events>
</global>
</config>
Then just write your observer implementation:
app/code/local/Danslo/RoundSpecialPrice/Model/Observer.php:
class Danslo_RoundSpecialPrice_Model_Observer
{
public function roundSpecialPrice($observer)
{
$product = $observer->getProduct();
if ($product->getSpecialPrice()) {
$product->setSpecialPrice(round($product->getSpecialPrice()));
}
}
public function roundSpecialPriceInCollection($observer)
{
foreach ($observer->getCollection() as $product) {
if ($product->getSpecialPrice()) {
$product->setSpecialPrice(round($product->getSpecialPrice()));
}
}
}
}

Answer 2

In PHP:
if (special price)
price = round(price);
Which database are you using? Maybe you could do this at database level and leave application intact. For example, if you use Firebird, you can use a computed field defined like this:
alter table prices
add customer_price
computed by (
case when special_price
then round(price,0)
else price
end)