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 $93.36   5.621%   $98.6078   $98.61   $98.60   $98.60  
  Purchase #2 $131.52   3.377%   $135.9614   $135.96   $135.95   $136.00  
  Purchase #3 $190.88   10.659%   $211.2259   $211.23   $211.25   $211.20  
  Purchase #4 $44.69   6.457%   $47.5756   $47.58   $47.60   $47.60  
  Purchase #5 $221.98   9.224%   $242.4554   $242.46   $242.45   $242.50  
  Purchase #6 $95.34   10.824%   $105.6596   $105.66   $105.65   $105.70  
  Purchase #7 $111.39   3.308%   $115.0748   $115.07   $115.05   $115.10  
  7 purchase totals = $889.16       $956.5605   $956.57   $956.55   $956.70