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 $194.56   8.198%   $210.51   $210.51   $210.50   $210.50  
  Purchase #2 $46.95   8.543%   $50.9609   $50.96   $50.95   $51.00  
  Purchase #3 $30.37   8.788%   $33.0389   $33.04   $33.05   $33.00  
  Purchase #4 $86.86   13.765%   $98.8163   $98.82   $98.80   $98.80  
  Purchase #5 $222.46   10.503%   $245.825   $245.83   $245.85   $245.80  
  Purchase #6 $224.92   5.266%   $236.7643   $236.76   $236.75   $236.80  
  Purchase #7 $73.81   9.246%   $80.6345   $80.63   $80.65   $80.60  
  7 purchase totals = $879.93       $956.5499   $956.55   $956.55   $956.50