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 $119.56   10.628%   $132.2668   $132.27   $132.25   $132.30  
  Purchase #2 $212.46   6.660%   $226.6098   $226.61   $226.60   $226.60  
  Purchase #3 $46.43   6.677%   $49.5301   $49.53   $49.55   $49.50  
  Purchase #4 $167.85   11.197%   $186.6442   $186.64   $186.65   $186.60  
  Purchase #5 $66.89   6.208%   $71.0425   $71.04   $71.05   $71.00  
  Purchase #6 $47.95   4.838%   $50.2698   $50.27   $50.25   $50.30  
  Purchase #7 $210.57   4.207%   $219.4287   $219.43   $219.45   $219.40  
  7 purchase totals = $871.71       $935.7919   $935.79   $935.80   $935.70