First, discounts and coupons are two different things. While coupons need to be added by customers during the checkout process, discounts are typically applied "automatically" depending on the conditions you're setting.
For what you seem to be wanting, discounts are the way to go. Read
the documentation here
on how to set up a discount. Note you can tailor a specific discount to apply to certain categories, products, and with the "restrictions" also to quantities and else. It's then logical that you'll need to set up multiple discounts, one for each set of conditions: for example, one with 10% for min qty 10pcs and max qty 49pcs, another one with 20% for min qty 50pcs and max qty 99pcs, and so on.
Oh, and please post a link here once your shop is on-line, so we can all go shopping and enjoy 100% discount! :woohoo:
