How to apply rounding rule in the 'rates definition' page.

I am using the salary basis as 'Determined by rates' for the auto calculation of salary components. In the 'rates definition' page, i need to the rates returned value as an integer applying the rounding rule to the ones digit.

eg: Basic is calculated as 40% of annual gross.

If the annual gross is Rs 40008, Basic becomes 1002.

The requirement is to round 1002 to 1000( by rounding the ones place to 0). Is it possible to achieve ?

Is there any way to create a custom rounding rule.