I found the answer on my own posted question titled 'eCart object - applying Discounts' from years ago where I asked the same questions (:.
(Ironically it was this date - July 18).
The answer:
you will need to create 2 separate discounts for this, the first one for 5 - 9 items:
Name: 5-9 items
Triggers:
"Subtotal For Any Column"
If the subtotal of column "Quantity" is ">" a value of "0"
AND
"Subtotal For Any Column"
If the subtotal of column "Quantity" is "<=" a value of "9"
Calculation:
"Based on cart subtotal"
cart Subtotal "times" "0.3"
the next one for 10 or more items:
Name: 10 or more items
Triggers:
"Subtotal For Any Column"
If the subtotal of column "Quantity" is ">=" a value of "10"
Calculation:
"Based on cart subtotal"
cart Subtotal "times" "0.5"