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 $210.36   3.109%   $216.9001   $216.90   $216.90   $216.90  
  Purchase #2 $118.47   9.685%   $129.9438   $129.94   $129.95   $129.90  
  Purchase #3 $112.39   5.156%   $118.1848   $118.18   $118.20   $118.20  
  Purchase #4 $191.30   12.574%   $215.3541   $215.35   $215.35   $215.40  
  Purchase #5 $107.78   12.207%   $120.9367   $120.94   $120.95   $120.90  
  Purchase #6 $244.41   6.854%   $261.1619   $261.16   $261.15   $261.20  
  Purchase #7 $12.45   8.382%   $13.4936   $13.49   $13.50   $13.50  
  7 purchase totals = $997.16       $1,075.9750   $1,075.96   $1,076.00   $1,076.00