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 $243.62   8.811%   $265.0854   $265.09   $265.10   $265.10  
  Purchase #2 $93.68   10.590%   $103.6007   $103.60   $103.60   $103.60  
  Purchase #3 $67.95   8.867%   $73.9751   $73.98   $74.00   $74.00  
  Purchase #4 $144.95   5.405%   $152.7845   $152.78   $152.80   $152.80  
  Purchase #5 $60.69   3.208%   $62.6369   $62.64   $62.65   $62.60  
  Purchase #6 $224.60   11.127%   $249.5912   $249.59   $249.60   $249.60  
  Purchase #7 $43.89   9.241%   $47.9459   $47.95   $47.95   $47.90  
  7 purchase totals = $879.38       $955.6197   $955.63   $955.70   $955.60