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 $202.43   6.509%   $215.6062   $215.61   $215.60   $215.60  
  Purchase #2 $243.91   11.418%   $271.7596   $271.76   $271.75   $271.80  
  Purchase #3 $119.55   8.138%   $129.279   $129.28   $129.30   $129.30  
  Purchase #4 $244.73   6.571%   $260.8112   $260.81   $260.80   $260.80  
  Purchase #5 $43.99   12.451%   $49.4672   $49.47   $49.45   $49.50  
  Purchase #6 $87.62   12.248%   $98.3517   $98.35   $98.35   $98.40  
  Purchase #7 $227.40   12.761%   $256.4185   $256.42   $256.40   $256.40  
  7 purchase totals = $1,169.63       $1,281.6934   $1,281.70   $1,281.65   $1,281.80