Lithuanian tipping etiquette can seem a bit confusing. While in other countries it’s perfectly normal and even courteous to say "thanks" (or the Lithuanian ačiū) and give a friendly nod when the waitstaff come to collect the bill, you may be startled to learn that in these parts it's an indication that you don’t want any change back.
This cultural slip-up can get a bit embarrassing, not to mention aggravating, if you're later forced to track down your server and ask for your change. This practice is slowly changing in Vilnius, but to avoid these situations it is suggested to only say "thank you" when the service of your waiter/waitress is no longer needed, when you're getting up to leave, or if you are happy for them to keep all of the change. When that’s not the case, try to avoid eye contact when they're taking the payment. The word you need learn is prašau (pronounced pra-show), meaning "please" or "here you are".
Despite the fact that standards of service have improved dramatically in the last decade, the average waiter or waitress in Lithuania still makes a paltry hourly sum, and a customary tip is up to 10% of the meal's total. So it is strongly encouraged to reward good service, when you feel it's deserved.
Finally, it's not common practice to add the tip to your credit card payment, in part because the company is highly unlikely to pass the tip on to the waitstaff. Most likely you will not even have an opportunity to leave a tip on your card. For that reason, try to have some change handy so you can still leave a cash tip, or ask your server for change if you need to.