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 $22.68   5.434%   $23.9124   $23.91   $23.90   $23.90  
  Purchase #2 $186.37   5.340%   $196.3222   $196.32   $196.30   $196.30  
  Purchase #3 $18.36   7.116%   $19.6665   $19.67   $19.65   $19.70  
  Purchase #4 $125.71   5.757%   $132.9471   $132.95   $132.95   $132.90  
  Purchase #5 $42.98   8.711%   $46.724   $46.72   $46.70   $46.70  
  Purchase #6 $201.95   12.609%   $227.4139   $227.41   $227.40   $227.40  
  Purchase #7 $107.80   9.628%   $118.179   $118.18   $118.20   $118.20  
  7 purchase totals = $705.85       $765.1651   $765.16   $765.10   $765.10