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 $59.66   11.646%   $66.608   $66.61   $66.60   $66.60  
  Purchase #2 $23.25   10.392%   $25.6661   $25.67   $25.65   $25.70  
  Purchase #3 $108.97   12.860%   $122.9835   $122.98   $123.00   $123.00  
  Purchase #4 $199.94   8.368%   $216.671   $216.67   $216.65   $216.70  
  Purchase #5 $59.66   5.804%   $63.1227   $63.12   $63.10   $63.10  
  Purchase #6 $113.66   7.255%   $121.906   $121.91   $121.90   $121.90  
  Purchase #7 $232.45   6.119%   $246.6736   $246.67   $246.65   $246.70  
  7 purchase totals = $797.59       $863.6309   $863.63   $863.55   $863.70