What type of computer system checks transactions of third parties in a pharmacy?

The correct choice is billing, as it specifically pertains to the processes used to handle financial transactions and verify payments for prescriptions and other pharmacy services. A billing system in a pharmacy facilitates the processing of insurance claims and manages interactions with third-party payers like insurance providers. This system ensures that the pharmacy receives accurate reimbursement for the medications dispensed and services provided, while also verifying patient eligibility and coverage for prescriptions.

Billing systems also help in tracking co-pays and deductibles, ensuring that the financial aspects of pharmacy transactions are properly managed. In this context, it is crucial for maintaining accurate records of transactions and ensuring compliance with various healthcare regulations, which is integral to the pharmacy's operations.