Spain. It is common to "round it off" as a tip around here, but not mandatory in any way. Examples:
You get a beer somewhere, it's 1.75€ and you round it off to 2€. That's a reasonable tip that says "service has been fine, thanks.".
You get dinner somewhere, it's 57.25€ and you round it to 60€. Same thing as above.
You get dinner somewhere, it's 57.25€ and you pay exactly that amount. The message is "the price was fair enough for what I got". Nobody will look badly at you.
You get dinner somewhere, it's 57.25€ and you pay 70€. The message is "you have been wonderful hosts, thank you VERY much".
Also, tips are not just for the service, but for the entire experience. You tip if you want to compliment the service, but also/alternatively because you want to compliment the food, or the ambient, or whatever.
You get a beer somewhere, it's 1.75€ and you round it off to 2€. That's a reasonable tip that says "service has been fine, thanks.".
You get dinner somewhere, it's 57.25€ and you round it to 60€. Same thing as above.
You get dinner somewhere, it's 57.25€ and you pay exactly that amount. The message is "the price was fair enough for what I got". Nobody will look badly at you.
You get dinner somewhere, it's 57.25€ and you pay 70€. The message is "you have been wonderful hosts, thank you VERY much".
Also, tips are not just for the service, but for the entire experience. You tip if you want to compliment the service, but also/alternatively because you want to compliment the food, or the ambient, or whatever.