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 $124.43   5.758%   $131.5947   $131.59   $131.60   $131.60  
  Purchase #2 $201.93   11.825%   $225.8082   $225.81   $225.80   $225.80  
  Purchase #3 $49.45   11.719%   $55.245   $55.25   $55.25   $55.20  
  Purchase #4 $213.54   11.193%   $237.4415   $237.44   $237.45   $237.40  
  Purchase #5 $180.28   3.527%   $186.6385   $186.64   $186.65   $186.60  
  Purchase #6 $21.42   9.299%   $23.4118   $23.41   $23.40   $23.40  
  Purchase #7 $130.75   3.647%   $135.5185   $135.52   $135.50   $135.50  
  7 purchase totals = $921.80       $995.6582   $995.66   $995.65   $995.50