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 $196.46   5.852%   $207.9568   $207.96   $207.95   $208.00  
  Purchase #2 $76.58   9.846%   $84.1201   $84.12   $84.10   $84.10  
  Purchase #3 $217.72   4.116%   $226.6814   $226.68   $226.70   $226.70  
  Purchase #4 $44.49   4.754%   $46.6051   $46.61   $46.60   $46.60  
  Purchase #5 $28.31   8.686%   $30.769   $30.77   $30.75   $30.80  
  Purchase #6 $209.92   5.257%   $220.9555   $220.96   $220.95   $221.00  
  Purchase #7 $78.73   6.387%   $83.7585   $83.76   $83.75   $83.80  
  7 purchase totals = $852.21       $900.8464   $900.86   $900.80   $901.00