oral_sex already implies it, fellatio and cunnilingus imply it through implying oral_sex.
I disagree with the others. Those two tags (anal, vaginal) are the broader groups -- '_fingering', '_penetration', and '_dildo' all go within them. Even having the '_penetration' tags alias to sex wouldn't work well, because Koekje recently collapsed the old '_insertion' tags into the '_penetration' ones, thus use of sex toys would fall into that group, including solo stuff.
Updated by anonymous