Unfortunatetly this option is not available at the moment, please accept my apologies about this. THe reason is that usually merchants want to specify a specific price for their products, instead of a price being changed automatically by a process that would typically not round the numbers to something that is communicated to customers. For instance, if you make a 5% discount on R14.95 item, the price would would be R14.2025. Most merchants don't want that, they want to specify the exact price (usually in that case they will set it at R13.95 or R14.2). The system cannot guess this, which is why this option is not available at the moment, please accept my apologies about this.
It is however possible to create discount codes with percentage if you would like.
Related questions:
> Can sales promotions be set by percentage instead of canceled prices?