According to the latest Scottish Retail Consortium figures, in June 2014 total Scottish sales decreased by 1.1% compared with June 2013, when they had increased by 2.8%.
Like-for-like sales decreased by 2.6% on last June, when they had increased by 0.3%.
Taking account of shop price deflation, June's total sales were up 0.7% in real terms, the highest real term growth this year, excluding January and Easter.
The figures released by the Scottish Retail Consortium and KPMG, show that food sales were down 1.4% on a total basis and by 3.3% on a like-for-like basis.
Meanwhile, total non-food sales decreased by 0.8% with like-for-like sales dropping 2% compared to June last year.
Although the figures represent a slight improvement on May, the SRC said they rounded off a weak second quarter.
SRC head of policy and external affairs David Martin said: "Warmer weather at the start of the month helped to get shoppers out, but as the weather cooled down so did sales.
"It is clear that cash conscious consumers have grown comfortable with value, especially on food, and continue to benefit from competitive pricing driven by stiff competition between the major grocery retailers. The continued decline in like-for-like food sales in June is suggestive that last month wasn't any different.
"Despite a slight set back in consumer confidence in June, overall consumer confidence has rebounded significantly throughout 2014 and where consumers have made savings, they now have the confidence to loosen their belts and increase spending on those discretionary non-food items.
"Fashion continues to benefit from this confidence, with clothing and footwear the best performing category in June and the only category to report positive total sales growth now for two consecutive months."