RETAIL sales topped $16 billion during May - a 10 per cent increase compared with the same period last year - despite a rise in interest rates and falling property values. But, after allowing for rising prices, the real growth in sales volume over the month was around three per cent compared with the previous year. A 23 per cent rise in the value of clothing and footwear and 13 per cent rise in volume helped spearheaded the increase, while foodstuffs rose by 11 per cent in value and nine per cent in volume. By comparison, sales of motor vehicles rose by about 10 per cent in value and around three per cent in volume. Enzio von Pfeil, chief regional economist for S G Warburg, said: ''Despite higher interest rates and a soggy property and stock market, the figures are quite good. ''I expect to see the figures liven up once the trade volumes begin to improve. This is likely to happen over the next quarter. They have already begun turning.'' Mr von Pfeil said that if the higher interest rates were discouraging expenditure then there was likely to be greater liquidity when pent-up demand was released. Connie Leung, senior economist for HSBC Asset Management, said: ''There has been a slowdown in retail sales. This could partly be because there is traditionally not big spending during May. We are hoping to see a turnaround in the latter half of the year.'' She added that rising shop rentals, passed on to the customer through higher prices, could also slow retail activity. There was virtually no change in the volume of supermarket sales during May, compared with the previous year, even though the value of sales rose by about eight per cent. Sales of fuel rose by six per cent in value and three per cent in volume. Department store sales of jewellery and watches increased by five per cent in value but volumes fell by more than one per cent. Sales of consumer durables, excluding cars and parts, also fell. The value of motor vehicles and parts rose by 9.5 per cent while volumes increased by 2.8 per cent. Compared with April, but not making allowances for seasonal factors, total retail sales rose by eight per cent in value and six per cent in volume. Over the period from January to May 1994, compared with the same period last year, sales rose by 16 per cent in value and nine per cent in volume.