Not able to default the Tax Classification code in the AR Transactions

Summary:

I associated the required Tax classification code at Customer Site Tax Profile and defined the default rules at "Manage Application Tax Options". Still the tax classification code is not defaulted. Experts, Can anyone suggest me.

Content (required):

I associated the required Tax classification code at Customer Site Tax Profile and defined the default rules at "Manage Application Tax Options". Still the tax classification code is not defaulted. Experts, Can anyone suggest me.

Version (include the version you are using, if applicable):

Code Snippet (add any code snippets that support your topic, if applicable):