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 $92.61   6.591%   $98.7139   $98.71   $98.70   $98.70  
  Purchase #2 $107.99   4.228%   $112.5558   $112.56   $112.55   $112.60  
  Purchase #3 $7.56   10.299%   $8.3386   $8.34   $8.35   $8.30  
  Purchase #4 $78.80   3.314%   $81.4114   $81.41   $81.40   $81.40  
  Purchase #5 $246.27   9.437%   $269.5105   $269.51   $269.50   $269.50  
  Purchase #6 $153.55   6.665%   $163.7841   $163.78   $163.80   $163.80  
  Purchase #7 $86.38   7.248%   $92.6408   $92.64   $92.65   $92.60  
  7 purchase totals = $773.16       $826.9551   $826.95   $826.95   $826.90