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 $56.87   4.762%   $59.5781   $59.58   $59.60   $59.60  
  Purchase #2 $118.73   5.859%   $125.6864   $125.69   $125.70   $125.70  
  Purchase #3 $198.43   5.325%   $208.9964   $209.00   $209.00   $209.00  
  Purchase #4 $224.74   12.550%   $252.9449   $252.94   $252.95   $252.90  
  Purchase #5 $229.53   8.542%   $249.1365   $249.14   $249.15   $249.10  
  Purchase #6 $222.65   6.696%   $237.5586   $237.56   $237.55   $237.60  
  Purchase #7 $35.62   9.162%   $38.8835   $38.88   $38.90   $38.90  
  7 purchase totals = $1,086.57       $1,172.7844   $1,172.79   $1,172.85   $1,172.80