I have developed the online store on magento platform. Everything works fine except the Catalog price rule for sale. I have created the simple rule that applies 15% discount
Extends lakshin-karunaratne answer above.
Make sure you move cataloguerule_apply_all away from midnight but not before catalog_product_index_price_reindex_all.
From "Solving Magento"
"Important is that rule prices must be calculated for the current day and before the catalog price re-indexing starts. Otherwise the observer will not get any active rule prices to augment the price index."
Therefore you would need to calculate the offset from GMT time to ensure both cataloguerule_apply_all and catalog_product_index_price_reindex_all are executed on the same day.
This can be easily achieved by using AOE Scheduler https://github.com/AOEpeople/Aoe_Scheduler