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 $24.82   4.783%   $26.0071   $26.01   $26.00   $26.00  
  Purchase #2 $187.47   10.158%   $206.5132   $206.51   $206.50   $206.50  
  Purchase #3 $179.50   3.836%   $186.3856   $186.39   $186.40   $186.40  
  Purchase #4 $100.89   11.648%   $112.6417   $112.64   $112.65   $112.60  
  Purchase #5 $72.50   8.379%   $78.5748   $78.57   $78.55   $78.60  
  Purchase #6 $23.36   13.711%   $26.5629   $26.56   $26.55   $26.60  
  Purchase #7 $133.73   13.685%   $152.031   $152.03   $152.05   $152.00  
  7 purchase totals = $722.27       $788.7163   $788.71   $788.70   $788.70