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 $250.46   6.199%   $265.986   $265.99   $266.00   $266.00  
  Purchase #2 $206.25   13.504%   $234.102   $234.10   $234.10   $234.10  
  Purchase #3 $179.83   13.293%   $203.7348   $203.73   $203.75   $203.70  
  Purchase #4 $118.79   12.433%   $133.5592   $133.56   $133.55   $133.60  
  Purchase #5 $142.51   11.200%   $158.4711   $158.47   $158.45   $158.50  
  Purchase #6 $57.56   3.559%   $59.6086   $59.61   $59.60   $59.60  
  Purchase #7 $11.75   6.605%   $12.5261   $12.53   $12.55   $12.50  
  7 purchase totals = $967.15       $1,067.9878   $1,067.99   $1,068.00   $1,068.00