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 $153.74   6.367%   $163.5286   $163.53   $163.55   $163.50  
  Purchase #2 $184.87   9.317%   $202.0943   $202.09   $202.10   $202.10  
  Purchase #3 $35.66   12.613%   $40.1578   $40.16   $40.15   $40.20  
  Purchase #4 $104.87   13.871%   $119.4165   $119.42   $119.40   $119.40  
  Purchase #5 $115.77   3.291%   $119.58   $119.58   $119.60   $119.60  
  Purchase #6 $126.80   12.772%   $142.9949   $142.99   $143.00   $143.00  
  Purchase #7 $54.61   13.296%   $61.8709   $61.87   $61.85   $61.90  
  7 purchase totals = $776.32       $849.6430   $849.64   $849.65   $849.70