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 $206.47   8.328%   $223.6648   $223.66   $223.65   $223.70  
  Purchase #2 $240.65   8.606%   $261.3603   $261.36   $261.35   $261.40  
  Purchase #3 $155.48   8.233%   $168.2807   $168.28   $168.30   $168.30  
  Purchase #4 $26.34   3.600%   $27.2882   $27.29   $27.30   $27.30  
  Purchase #5 $136.67   7.334%   $146.6934   $146.69   $146.70   $146.70  
  Purchase #6 $48.92   13.203%   $55.3789   $55.38   $55.40   $55.40  
  Purchase #7 $171.39   9.819%   $188.2188   $188.22   $188.20   $188.20  
  7 purchase totals = $985.92       $1,070.8851   $1,070.88   $1,070.90   $1,071.00