Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $56.42   8.597%   $61.2704   $61.27   $61.25   $61.30  
  Purchase #2 $243.50   7.224%   $261.0904   $261.09   $261.10   $261.10  
  Purchase #3 $136.86   12.803%   $154.3822   $154.38   $154.40   $154.40  
  Purchase #4 $119.27   9.117%   $130.1438   $130.14   $130.15   $130.10  
  Purchase #5 $204.52   13.862%   $232.8706   $232.87   $232.85   $232.90  
  Purchase #6 $25.48   6.427%   $27.1176   $27.12   $27.10   $27.10  
  Purchase #7 $209.35   7.439%   $224.9235   $224.92   $224.90   $224.90  
  7 purchase totals = $995.40       $1,091.7985   $1,091.79   $1,091.75   $1,091.80