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 $46.48   8.783%   $50.5623   $50.56   $50.55   $50.60  
  Purchase #2 $104.35   9.209%   $113.9596   $113.96   $113.95   $114.00  
  Purchase #3 $50.81   7.692%   $54.7183   $54.72   $54.70   $54.70  
  Purchase #4 $173.67   11.317%   $193.3242   $193.32   $193.30   $193.30  
  Purchase #5 $133.76   4.399%   $139.6441   $139.64   $139.65   $139.60  
  Purchase #6 $101.69   10.637%   $112.5068   $112.51   $112.50   $112.50  
  Purchase #7 $20.78   11.553%   $23.1807   $23.18   $23.20   $23.20  
  7 purchase totals = $631.54       $687.8960   $687.89   $687.85   $687.90