New figures from the Central Statistics Office show that the volume of retail sales decreased by 4.7% in August compared to July.
But on an annual basis, the volume of retail sales rose by 5.2%, the CSO added.
The CSO said that on a monthly basis, the volume of motor sales slowed down by over 11% after new car registrations had caused a spike in volumes in July.
Sales in department stores were also down 1.1% on a monthly basis.
However, the volume of sales in the furniture and lighting sectors rose by 8.8%, while other retail sales increased by 5.1% and sales of hardware, paints and glass increased by 4.6% in August.
The CSO said that when car sales are excluded from the figures, the volume of retail sales rose by 0.9% in August on a monthly basis and by 4.1% on an annual basis.
Commenting on today's figures, Merrion economist Austin Hughes said that although retail sales remain erratic on a monthly basis, the underlying trend is still positive.
"While most attention was on cars last year and will be again in 2016, personal spending in other areas has generally picked up in recent months and is becoming more broad-based. This can only be good news for retailers and employment prospects in the sector," the economist stated.
But he noted that the Brexit fall-out and the uncertain economic implications will likely impact negatively on Irish consumer sentiment, resulting in lower personal spending going forward.
"Furthermore, a sharp fall in the pound may well entice Irish shoppers to spend in Northern Ireland," he added.