Use IIS URL Rewrite Module rule to remove trailing slashes from URLs.
<!-- ... -->
<system.webServer>
<rewrite>
<rules>
<!-- To always remove trailing slash from the URL -->
<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>
</rules>
</rewrite>
</system.webServer>
<!-- ... -->