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 $235.94   10.571%   $260.8812   $260.88   $260.90   $260.90  
  Purchase #2 $154.57   7.164%   $165.6434   $165.64   $165.65   $165.60  
  Purchase #3 $221.50   3.724%   $229.7487   $229.75   $229.75   $229.70  
  Purchase #4 $244.95   9.670%   $268.6367   $268.64   $268.65   $268.60  
  Purchase #5 $214.35   13.666%   $243.6431   $243.64   $243.65   $243.60  
  Purchase #6 $246.89   7.455%   $265.2956   $265.30   $265.30   $265.30  
  Purchase #7 $152.73   9.745%   $167.6135   $167.61   $167.60   $167.60  
  7 purchase totals = $1,470.93       $1,601.4622   $1,601.46   $1,601.50   $1,601.30