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 $58.34   9.159%   $63.6834   $63.68   $63.70   $63.70  
  Purchase #2 $168.59   13.221%   $190.8793   $190.88   $190.90   $190.90  
  Purchase #3 $200.97   7.168%   $215.3755   $215.38   $215.40   $215.40  
  Purchase #4 $198.76   12.835%   $224.2708   $224.27   $224.25   $224.30  
  Purchase #5 $157.76   5.485%   $166.4131   $166.41   $166.40   $166.40  
  Purchase #6 $95.28   6.648%   $101.6142   $101.61   $101.60   $101.60  
  Purchase #7 $44.44   3.456%   $45.9758   $45.98   $46.00   $46.00  
  7 purchase totals = $924.14       $1,008.2121   $1,008.21   $1,008.25   $1,008.30