Way to track sales of a computer shop?

Way to track sales of a computer shop?

Hello.

I work for a computer service / computers shop and printer outlet shop here in Romania. We started using the Zoho CRM (only Free Edition for the moment) in order to keep better track of our sales, customers, and service task history.
We started keeping the Service actions as tasks and fully customised the layout in order to describe the problem, get task status, and everything else.
Now, we want to integrate sales tracking into the CRM and I want to be able to differentiate them. The problem is, I can't add the sales as Tasks (with a different subject) because I have set up a field that assigns numbers to all service tasks. Therefore, I don't want service task numbers to be mixed up by Sales numbers like this :
104 is a deffective laptop, and 105 to 165 are sales, then it's another deffective laptop.
Is there any way you would suggest of me keeping track of sales and service actions not mixing up? Maybe I can get some extra feature to help me with this if I upgrade to a paid subscription ? Please help me!

Looking forward in your replies!

Cheers all, 
Horia