Scaling discount strategy?

My store currently has a scaling discount based on cart total.

$20 – 5% off cart total $50 – 10% off cart total $80 – 15% off cart total $110 – 20% off cart total

Is this a good template? Is there any general recommendations?

What kind of discounts to you offer?

I know this might vary depending on general prices of products in your store. My catalog's prices range from $5-50 with the average being around $15-20.