YES

(VAR x y)
(RULES
  a(a(z(),x),a(z(),y)) -> a(x,a(a(z(),x),y))
  a(a(z(),x),z()) -> a(x,a(z(),z()))
  s(x) -> a(z(),x)
)

(COMMENT
Termination is shown by KBO with weight

  w0 = 1
  w(a) = 0
  w(z) = 1
  w(s) = 2

and precedence:

  s > a > z
)