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 $92.87   12.102%   $104.1091   $104.11   $104.10   $104.10  
  Purchase #2 $229.45   3.231%   $236.8635   $236.86   $236.85   $236.90  
  Purchase #3 $19.99   13.127%   $22.6141   $22.61   $22.60   $22.60  
  Purchase #4 $12.74   7.366%   $13.6784   $13.68   $13.70   $13.70  
  Purchase #5 $176.30   8.123%   $190.6208   $190.62   $190.60   $190.60  
  Purchase #6 $157.75   12.449%   $177.3883   $177.39   $177.40   $177.40  
  Purchase #7 $47.31   3.615%   $49.0203   $49.02   $49.00   $49.00  
  7 purchase totals = $736.41       $794.2945   $794.29   $794.25   $794.30