I know we have the ability to choose tipping levels (up to three); however I have come across a processor who is able to change from $ amount to % levels.
For example:
We know that we would like the customers to tip at lease $3. So, we set it up so that if the subtotal is more than $30, the suggested tip levels are 10%($3+), 15% and 18%; however for subtotals below $30 the tip levels are $3, $5, $7. there is always custom at the end for both scenarios and the 1st tip level is always default. Most people don't change the default tip (at least in our area).
I thought this was genius and worthy of developing on city hive.