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 $93.77   11.560%   $104.6098   $104.61   $104.60   $104.60  
  Purchase #2 $41.78   13.119%   $47.2611   $47.26   $47.25   $47.30  
  Purchase #3 $26.82   9.825%   $29.4551   $29.46   $29.45   $29.50  
  Purchase #4 $71.36   5.313%   $75.1514   $75.15   $75.15   $75.20  
  Purchase #5 $250.49   10.735%   $277.3801   $277.38   $277.40   $277.40  
  Purchase #6 $112.71   8.622%   $122.4279   $122.43   $122.45   $122.40  
  Purchase #7 $199.96   3.483%   $206.9246   $206.92   $206.90   $206.90  
  7 purchase totals = $796.89       $863.2100   $863.21   $863.20   $863.30