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 $34.56   11.290%   $38.4618   $38.46   $38.45   $38.50  
  Purchase #2 $242.58   4.457%   $253.3918   $253.39   $253.40   $253.40  
  Purchase #3 $159.71   3.565%   $165.4037   $165.40   $165.40   $165.40  
  Purchase #4 $135.74   13.286%   $153.7744   $153.77   $153.75   $153.80  
  Purchase #5 $59.74   5.533%   $63.0454   $63.05   $63.05   $63.00  
  Purchase #6 $51.92   13.693%   $59.0294   $59.03   $59.05   $59.00  
  Purchase #7 $59.42   9.302%   $64.9472   $64.95   $64.95   $64.90  
  7 purchase totals = $743.67       $798.0537   $798.05   $798.05   $798.00