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 $42.28   11.219%   $47.0234   $47.02   $47.00   $47.00  
  Purchase #2 $173.81   9.316%   $190.0021   $190.00   $190.00   $190.00  
  Purchase #3 $247.85   5.688%   $261.9477   $261.95   $261.95   $261.90  
  Purchase #4 $196.39   6.773%   $209.6915   $209.69   $209.70   $209.70  
  Purchase #5 $85.39   11.873%   $95.5284   $95.53   $95.55   $95.50  
  Purchase #6 $22.66   3.417%   $23.4343   $23.43   $23.45   $23.40  
  Purchase #7 $176.93   6.248%   $187.9846   $187.98   $188.00   $188.00  
  7 purchase totals = $945.31       $1,015.6120   $1,015.60   $1,015.65   $1,015.50