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 $64.49   13.433%   $73.1529   $73.15   $73.15   $73.20  
  Purchase #2 $191.56   13.111%   $216.6754   $216.68   $216.70   $216.70  
  Purchase #3 $38.95   5.335%   $41.028   $41.03   $41.05   $41.00  
  Purchase #4 $224.89   13.632%   $255.547   $255.55   $255.55   $255.50  
  Purchase #5 $111.60   8.674%   $121.2802   $121.28   $121.30   $121.30  
  Purchase #6 $105.81   3.260%   $109.2594   $109.26   $109.25   $109.30  
  Purchase #7 $71.71   3.550%   $74.2557   $74.26   $74.25   $74.30  
  7 purchase totals = $809.01       $891.1986   $891.21   $891.25   $891.30