nginx as a reverse caching proxy

Question

Is it caching static content? I check the /tmp dir where the location is set but it's empty.

nginx.conf

user  nobody;
# no need for more workers in the proxy mode
worker_processes  1;
error_log  /var/log/nginx/error.log info;
worker_rlimit_nofile 20480;
events {
 worker_connections 5120; # increase for busier servers
 use epoll; # you should use epoll here for Linux kernels 2.6.x
}
http {
 server_name_in_redirect off;
 server_names_hash_max_size 2048;
 server_names_hash_bucket_size 256;
 include    mime.types;
 default_type  application/octet-stream;
 server_tokens off;
 sendfile on;
 tcp_nopush on;
 tcp_nodelay on;
 keepalive_timeout  60;
 gzip on;
 gzip_vary on;
 gzip_disable "MSIE [1-6]\.";
 gzip_proxied any;
 gzip_http_version 1.1;
 gzip_min_length  0;
 gzip_comp_level  6;
 gzip_buffers  16 8k;
# You can remove image/png image/x-icon image/gif image/jpeg if you have slow CPU
 gzip_types    text/* image/png image/x-icon image/gif image/jpeg application/*;
 ignore_invalid_headers on;
 client_header_timeout  3m;
 client_body_timeout 3m;
 send_timeout     3m;
 reset_timedout_connection on;
 connection_pool_size  256;
 client_header_buffer_size 256k;
 large_client_header_buffers 4 256k;
 client_max_body_size 4M; 
 client_body_buffer_size 128k;
 request_pool_size  32k;
 output_buffers   4 32k;
 postpone_output  1460;
 proxy_cache_path  /tmp/nginx_proxy levels=1:2 keys_zone=my-cache:8m max_size=1000m inactive=600m;
 proxy_temp_path  /tmp/nginx_proxy/;
 client_body_in_file_only on;
 log_format bytes_log "$msec $bytes_sent .";
 include "/etc/nginx/vhosts/*";
}

site.com

server {
          error_log /var/log/nginx/vhost-error_log warn;
          listen IP.IP.IP.IP:80;
          server_name site.com www.site.com;
          access_log /usr/local/apache/domlogs/site.com-bytes_log bytes_log;
          access_log /usr/local/apache/domlogs/site.com combined;
          root /home/site.com/public_html;
          location / {
          location ~.*\.(3gp|gif|jpg|jpeg|png|ico|wmv|avi|asf|asx|mpg|mpeg|mp4|pls|mp3|mid|wav|swf|flv|html|htm|txt|js|css|exe|zip|tar|rar|gz|tgz|bz2|uha|7z|doc|docx|xls|xlsx|pdf|iso)$ {
          expires 7d;
          try_files $uri @backend;
          }
          error_page 405 = @backend;
          add_header X-Cache "HIT from Backend";
          proxy_pass http://IP.IP.IP.IP:8080;
          include proxy.inc;
          }
          location @backend {
          internal;
          proxy_pass http://IP.IP.IP.IP:8080;
          include proxy.inc;
          }
          location ~ .*\.(php|jsp|cgi|pl|py)?$ {
          proxy_pass http://IP.IP.IP.IP:8080;
          include proxy.inc;
          }
          location ~ /\.ht {
          deny all;
          }
        }

proxy.inc

    proxy_connect_timeout 30s;
proxy_send_timeout   90;
proxy_read_timeout   90;
proxy_buffer_size    64k;
proxy_buffers     16 32k;
proxy_busy_buffers_size 64k;
#proxy_pass http://127.0.0.1:81;
proxy_cache my-cache;
proxy_cache_valid  200 302  60m;
proxy_cache_valid  404      1m;
proxy_pass_header Set-Cookie;
proxy_redirect     off;
proxy_hide_header  Vary;
proxy_set_header   Accept-Encoding '';
proxy_ignore_headers Cache-Control Expires;
proxy_set_header   Referer $http_referer;
proxy_set_header   Host   $host;
proxy_set_header   Cookie $http_cookie;
proxy_set_header   X-Real-IP  $remote_addr;
proxy_set_header   X-Forwarded-For $proxy_add_x_forwarded_for;