Do we pay tips to package a delivering person?

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I was not used to paying tips in my country until I got to US where almost every service we have to pay tips of 10-15% at least. Sometimes I do forgot to Pay tips when I visit the restaurant as it was not something I use to do. Yesterday a package delivering guy send in a package and I wonder if we need to pay them tips? How much is appropriate? Does other countries need to pay tips for the services as well?