Try the following:

(defun nxml-jump-to-closing-tag ()
  (interactive)
  (forward-char 2)
  (if (search-backward "<" nil t)
      (nxml-forward-element)
    (message "No more elements")
    )
  )

(defun nxml-jump-to-openning-tag ()
  (interactive)
  (backward-char 2)
  (if (search-forward ">" nil t)
      (nxml-backward-element)
    (message "No more elements")
    )
  )

(define-key nxml-mode-map (kbd "<C-M-right>") 'nxml-jump-to-closing-tag)
(define-key nxml-mode-map (kbd "<C-M-left>") 'nxml-jump-to-openning-tag)

Press C-M-←. Press C-M-→ to get back.

Try the following:

(defun nxml-jump-to-closing-tag ()
  (interactive)
  (forward-char 2)
  (if (search-backward "<" nil t)
      (nxml-forward-element)
    (message "No more elements")
    )
  )

(defun nxml-jump-to-openning-tag ()
  (interactive)
  (backward-char 2)
  (if (search-forward ">" nil t)
      (nxml-backward-element)
    (message "No more elements")
    )
  )

(define-key nxml-mode-map (kbd "<C-M-right>") 'nxml-jump-to-closing-tag)
(define-key nxml-mode-map (kbd "<C-M-left>")  'nxml-jump-to-openning-tag)

Press C-M-←. Press C-M-→ to get back.

Put the point in the end of the tag:

<a>
  <b>...</b>
</a>▌

and press C-m-←. Press C-m-→ to get back.

Try the following:

(defun nxml-jump-to-closing-tag ()
  (interactive)
  (forward-char 2)
  (if (search-backward "<" nil t)
      (nxml-forward-element)
    (message "No more elements")
    )
  )

(defun nxml-jump-to-openning-tag ()
  (interactive)
  (backward-char 2)
  (if (search-forward ">" nil t)
      (nxml-backward-element)
    (message "No more elements")
    )
  )

(define-key nxml-mode-map (kbd "<C-M-right>") 'nxml-jump-to-closing-tag)
(define-key nxml-mode-map (kbd "<C-M-left>") 'nxml-jump-to-openning-tag)

Press C-M-←. Press C-M-→ to get back.