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 $58.85   6.507%   $62.6794   $62.68   $62.70   $62.70  
  Purchase #2 $91.56   10.647%   $101.3084   $101.31   $101.30   $101.30  
  Purchase #3 $101.46   10.513%   $112.1265   $112.13   $112.15   $112.10  
  Purchase #4 $238.57   9.433%   $261.0743   $261.07   $261.05   $261.10  
  Purchase #5 $109.46   5.856%   $115.87   $115.87   $115.85   $115.90  
  Purchase #6 $150.91   11.287%   $167.9432   $167.94   $167.95   $167.90  
  Purchase #7 $59.27   3.190%   $61.1607   $61.16   $61.15   $61.20  
  7 purchase totals = $810.08       $882.1625   $882.16   $882.15   $882.20