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 $86.38   8.308%   $93.5565   $93.56   $93.55   $93.60  
  Purchase #2 $245.90   8.381%   $266.5089   $266.51   $266.50   $266.50  
  Purchase #3 $177.99   4.656%   $186.2772   $186.28   $186.30   $186.30  
  Purchase #4 $40.42   4.535%   $42.253   $42.25   $42.25   $42.30  
  Purchase #5 $46.31   4.593%   $48.437   $48.44   $48.45   $48.40  
  Purchase #6 $155.33   9.147%   $169.538   $169.54   $169.55   $169.50  
  Purchase #7 $73.97   12.243%   $83.0261   $83.03   $83.05   $83.00  
  7 purchase totals = $826.30       $889.5967   $889.61   $889.65   $889.60