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 $23.85   9.817%   $26.1914   $26.19   $26.20   $26.20  
  Purchase #2 $169.76   7.421%   $182.3579   $182.36   $182.35   $182.40  
  Purchase #3 $202.57   12.462%   $227.8143   $227.81   $227.80   $227.80  
  Purchase #4 $68.42   4.348%   $71.3949   $71.39   $71.40   $71.40  
  Purchase #5 $43.25   7.382%   $46.4427   $46.44   $46.45   $46.40  
  Purchase #6 $58.76   5.693%   $62.1052   $62.11   $62.10   $62.10  
  Purchase #7 $196.48   11.105%   $218.2991   $218.30   $218.30   $218.30  
  7 purchase totals = $763.09       $834.6055   $834.60   $834.60   $834.60