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 $246.97   5.844%   $261.4029   $261.40   $261.40   $261.40  
  Purchase #2 $214.46   9.362%   $234.5377   $234.54   $234.55   $234.50  
  Purchase #3 $51.51   9.613%   $56.4617   $56.46   $56.45   $56.50  
  Purchase #4 $54.79   8.446%   $59.4176   $59.42   $59.40   $59.40  
  Purchase #5 $123.70   13.573%   $140.4898   $140.49   $140.50   $140.50  
  Purchase #6 $65.74   11.356%   $73.2054   $73.21   $73.20   $73.20  
  Purchase #7 $93.39   8.183%   $101.0321   $101.03   $101.05   $101.00  
  7 purchase totals = $850.56       $926.5472   $926.55   $926.55   $926.50