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 $217.78   13.680%   $247.5723   $247.57   $247.55   $247.60  
  Purchase #2 $130.31   4.438%   $136.0932   $136.09   $136.10   $136.10  
  Purchase #3 $163.64   5.786%   $173.1082   $173.11   $173.10   $173.10  
  Purchase #4 $166.74   10.307%   $183.9259   $183.93   $183.95   $183.90  
  Purchase #5 $61.87   9.371%   $67.6678   $67.67   $67.65   $67.70  
  Purchase #6 $179.90   13.546%   $204.2693   $204.27   $204.25   $204.30  
  Purchase #7 $43.33   8.328%   $46.9385   $46.94   $46.95   $46.90  
  7 purchase totals = $963.57       $1,059.5752   $1,059.58   $1,059.55   $1,059.60