Admin can set discount rules based on Tiers ( Quantity tier, Amount tier & Weight Tier ).

For ex.
Tier 1) Buy 1 to 5 T-Shirts Get 20% Off.
Tier 2) Buy 6 to 10 T-Shirts Get 25% Off.
You can make such more tiers as you wants.

For making this discount rule select Discount Rules tab.
Now choose Product Rules
Now you can choose Add Tier Rule for Product ( to make discount rule on a particular product ) or Add Tier Rule for Category ( to make discount rule based on a particular category ).

Fill Rule, Restrictions and Validity tabs accordingly.
After saving the rule it can be seen in the given table below.

Now you have to give permission to your rule to give discount on the product or category you have chosen.
Click on the Setting Tab.
Check Tier Rule or/and Tier Category Rule as shown below.

After checking these rules, Choose among First Match Rule, Best Match Rule or All Match Rule and click on save rule button below.

Now your Rules are active and if anyone buy the product which you have chosen they will get discount.
The Discount can be seen on the shop page as well as on product page.

The discount can be shown in the cart if the products are added to the cart as in the given picture below.

As you increase the quantity and it matches your tier quantity the discount amount changes as follows

Now whenever you want to disable this discount rule, you don’t have to delete it, just go to Setting Tab and uncheck this rule.