State sales tax revenues decreased by more than 3.5 percent in fiscal 2010, according to figures released this week by the Iowa Department of Revenue. The total retail sales tax due on returns filed for the fiscal year that ended June 30 was $1.91 billion, down 3.54 percent from the $1.98 billion collected in fiscal 2009. The number of quarterly returns filed decreased to 350,870 in fiscal 2010 from 352,178 in fiscal year 2009, a 0.4 percent decrease. Businesses that had $1 million or more in quarterly gross sales collected 65.3 percent of total retail sales tax in fiscal 2010, while comprising only 3.9 percent of total businesses filing returns, according to the report. Firms with quarterly gross sales under $10,000 represented nearly 50 percent of total businesses filing returns, but their collective sales tax payments represented just 1.1 percent of the total tax collections.