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 $41.77   10.144%   $46.0071   $46.01   $46.00   $46.00  
  Purchase #2 $140.39   5.158%   $147.6313   $147.63   $147.65   $147.60  
  Purchase #3 $135.53   5.226%   $142.6128   $142.61   $142.60   $142.60  
  Purchase #4 $171.79   13.316%   $194.6656   $194.67   $194.65   $194.70  
  Purchase #5 $17.99   7.177%   $19.2811   $19.28   $19.30   $19.30  
  Purchase #6 $217.41   13.759%   $247.3234   $247.32   $247.30   $247.30  
  Purchase #7 $33.84   5.577%   $35.7273   $35.73   $35.75   $35.70  
  7 purchase totals = $758.72       $833.2486   $833.25   $833.25   $833.20