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 $58.81   11.223%   $65.4102   $65.41   $65.40   $65.40  
  Purchase #2 $63.81   10.529%   $70.5286   $70.53   $70.55   $70.50  
  Purchase #3 $242.36   8.128%   $262.059   $262.06   $262.05   $262.10  
  Purchase #4 $43.93   7.113%   $47.0547   $47.05   $47.05   $47.10  
  Purchase #5 $67.26   13.226%   $76.1558   $76.16   $76.15   $76.20  
  Purchase #6 $153.36   6.208%   $162.8806   $162.88   $162.90   $162.90  
  Purchase #7 $27.79   9.215%   $30.3508   $30.35   $30.35   $30.40  
  7 purchase totals = $657.32       $714.4397   $714.44   $714.45   $714.60