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 $232.96   5.586%   $245.9731   $245.97   $245.95   $246.00  
  Purchase #2 $41.56   3.445%   $42.9917   $42.99   $43.00   $43.00  
  Purchase #3 $56.34   5.593%   $59.4911   $59.49   $59.50   $59.50  
  Purchase #4 $196.53   5.863%   $208.0526   $208.05   $208.05   $208.10  
  Purchase #5 $73.37   8.594%   $79.6754   $79.68   $79.70   $79.70  
  Purchase #6 $89.82   3.239%   $92.7293   $92.73   $92.75   $92.70  
  Purchase #7 $228.64   9.683%   $250.7792   $250.78   $250.80   $250.80  
  7 purchase totals = $919.22       $979.6924   $979.69   $979.75   $979.80