فِي كُلِّ تَرْوِيحَةٍ تَسْلِيمَتَانِ
Translation: Each tarwihah contains two salams.
Each four-rakah tarwihah is prayed as two rakahs followed by salam, then two more rakahs followed by salam. Twenty rakahs therefore ordinarily contain ten salams.
Five tarwihahs do not mean five salams: each group of four consists of two separate two-rakah prayers.