You don't say if this is a generic discount, or discount for a specific category or item.
Lets say it is for item whose ID = 1
The standard price is $64.99
for 4-23 items, there is a $5 unit discount
for 24-99 items, there is a $10 unit discount
In the ecart object, under discounts, set up a rule called $5 per item discount
under trigger add
quantity of item 1 in the cart > a value of 3
add a second trigger
quantity of item 1 in the cart < a value of 24
calculation is based on the quantity of an item, the quantity of item 1 times 5.
This will apply a $5 discount on every instance of item 1 in the cart, as long as the quantity is between 4 and 23
Repeat the same logic for 24-99