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 $60.90   11.868%   $68.1276   $68.13   $68.15   $68.10  
  Purchase #2 $186.98   9.503%   $204.7487   $204.75   $204.75   $204.70  
  Purchase #3 $235.92   10.749%   $261.279   $261.28   $261.30   $261.30  
  Purchase #4 $163.36   6.256%   $173.5798   $173.58   $173.60   $173.60  
  Purchase #5 $42.77   10.464%   $47.2455   $47.25   $47.25   $47.20  
  Purchase #6 $64.60   12.581%   $72.7273   $72.73   $72.75   $72.70  
  Purchase #7 $153.49   7.340%   $164.7562   $164.76   $164.75   $164.80  
  7 purchase totals = $908.02       $992.4641   $992.48   $992.55   $992.40