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 $49.41   3.583%   $51.1804   $51.18   $51.20   $51.20  
  Purchase #2 $181.83   7.351%   $195.1963   $195.20   $195.20   $195.20  
  Purchase #3 $166.46   5.335%   $175.3406   $175.34   $175.35   $175.30  
  Purchase #4 $82.66   10.392%   $91.25   $91.25   $91.25   $91.30  
  Purchase #5 $250.30   6.416%   $266.3592   $266.36   $266.35   $266.40  
  Purchase #6 $28.51   7.403%   $30.6206   $30.62   $30.60   $30.60  
  Purchase #7 $45.26   3.648%   $46.9111   $46.91   $46.90   $46.90  
  7 purchase totals = $804.43       $856.8582   $856.86   $856.85   $856.90