There is a internal method for check verification.
From the Help Guide.
The Checks command is designed for those businesses that are not using an outside service for check verification. Store Operations can provide a positive or negative check verification scheme.
To define which method to use, go to the Database menu, click Tender Types, select the Check tender, click Properties, click the Verification tab, and then select the applicable option under the Check Verification heading.
When you click Checks, you will see a list of check accounts. You can click New to add a check account; click Properties to revise the selected check account; click Delete to remove the selected check account from the database; or click Copy to copy values from an existing record.
A positive check file holds the names of those people whose checks may be accepted, unless otherwise noted. A negative check file holds the names of those people whose checks are not to be accepted. Store Operations will check the account number entered by the cashier against the account numbers contained in the check file to determine if the check can be accepted.
In most cases, negative check verification is used. Using this method, all checks will be accepted at the point-of-sale for the first time. Later, if a check bounces, you can use the Checks menu option to enter the appropriate status. When the customer attempts to pass a check a second time, the cashier will instantly see that there is a problem.
When you click New or Properties, you will see the Check Properties window that enables you to define/modify the check properties. The fields in this window are described below.
Account number: The checking account number. This number may include up to 30 characters.
Account name: The name of the checkholder. This account name account name may include up to 30 characters, and is optional.
Status codes: When Store Operations encounters a check that matches the specified account number, it will display a message containing the status code to the cashier. You can use the status codes 4 to 8 for in-store security codes. For example, status code 5 may signify a hidden "Call Police" code.
Alternatively, you can check with your processor to see if they offer check verification processing. This way you can process the check at the time of sell and make sure you get paid. Then their is no reason to record check information.