Under Level 5 of the Plan for Living with COVID-19, only essential retail outlets will remain open.
S.I. No. 448 of 2020 Health Act 1947 (Section 31A - Temporary Restrictions) (COVID-19) (No. 8) Regulations 2020 clearly sets out the temporary restrictions under Level 5.
A list of essential retail outlets at Level 5 can be found at https://www.gov.ie/en/publication/60ecc-essential-retail-outlets-for-level-5.
This includes "Any other retail outlet that operates an online or other remote system of ordering goods for purposes of collection at the retail outlet."
So yes a worker can attend work outside of the 5 km limit to pack orders for collection or delivery. You should note that taking orders and other administrative tasks in relation to this business should be undertaken from home.
It is important to check gov.ie for the latest information, public health advice and guidelines from Government in relation to COVID-19.