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 $63.93   5.209%   $67.2601   $67.26   $67.25   $67.30  
  Purchase #2 $6.71   11.453%   $7.4785   $7.48   $7.50   $7.50  
  Purchase #3 $230.48   13.498%   $261.5902   $261.59   $261.60   $261.60  
  Purchase #4 $49.86   8.102%   $53.8997   $53.90   $53.90   $53.90  
  Purchase #5 $198.69   13.129%   $224.776   $224.78   $224.80   $224.80  
  Purchase #6 $146.45   12.458%   $164.6947   $164.69   $164.70   $164.70  
  Purchase #7 $109.45   5.791%   $115.7882   $115.79   $115.80   $115.80  
  7 purchase totals = $805.57       $895.4874   $895.49   $895.55   $895.60