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 $91.66   10.545%   $101.3255   $101.33   $101.35   $101.30  
  Purchase #2 $225.39   4.829%   $236.2741   $236.27   $236.25   $236.30  
  Purchase #3 $131.60   5.233%   $138.4866   $138.49   $138.50   $138.50  
  Purchase #4 $85.81   10.747%   $95.032   $95.03   $95.05   $95.00  
  Purchase #5 $76.76   10.614%   $84.9073   $84.91   $84.90   $84.90  
  Purchase #6 $36.57   3.555%   $37.8701   $37.87   $37.85   $37.90  
  Purchase #7 $248.28   5.781%   $262.6331   $262.63   $262.65   $262.60  
  7 purchase totals = $896.07       $956.5287   $956.53   $956.55   $956.50