Why not? You’re rounding $21.40 to $20.00. You can round $129.00 to $120… or any amount to a fixed amount. All of them are discounts eventually.
They are separated by accounts.
btw receivables account balance should display the amount you expected to receive. Discounts should go to related discount accounts. I think you mean debiting the discount account.
As encountered on most businesses I think a lot of SambaPOS users negotiates price with customer and use discount or rounding option to bring ticket amount to that price. However if you really need a second type of rounding to differ roundings more than 0.99 you have a lot of manual or automated options. This tutorial might be a good start.
PS: For almost 10 years any kind of discounting methods being used across the world discussed by the community and I’m very confident of the qualification of such common SambaPOS functions. However I can not say SambaPOS will make everyone happy. Of course some people will like features of other POS and use it.
However we never implemented a feature just because it exists on other POS. We discuss all new features here and implement if it is useful for people. So instead of demotivating us by constantly mentioning other POS you can prefer to be a part of the community and try to explain how “that option” will be useful for SambaPOS users.