Use URL Rewrite 2:
<rule name="Remove trailing slash" stopProcessing="true"> <match url="(.*)/$" /> <conditions> <add input="{REQUEST_FILENAME}" matchType="IsFile" negate="true" /> <add input="{REQUEST_FILENAME}" matchType="IsDirectory" negate="true" /> </conditions> <action type="Redirect" redirectType="Permanent" url="{R:1}" /> </rule>