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 $151.81   7.801%   $163.6527   $163.65   $163.65   $163.70  
  Purchase #2 $67.93   12.347%   $76.3173   $76.32   $76.30   $76.30  
  Purchase #3 $14.84   10.132%   $16.3436   $16.34   $16.35   $16.30  
  Purchase #4 $214.91   10.423%   $237.3101   $237.31   $237.30   $237.30  
  Purchase #5 $121.41   3.233%   $125.3352   $125.34   $125.35   $125.30  
  Purchase #6 $207.81   9.243%   $227.0179   $227.02   $227.00   $227.00  
  Purchase #7 $67.66   9.274%   $73.9348   $73.93   $73.95   $73.90  
  7 purchase totals = $846.37       $919.9116   $919.91   $919.90   $919.80