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 $60.83   9.486%   $66.6003   $66.60   $66.60   $66.60  
  Purchase #2 $48.78   10.142%   $53.7273   $53.73   $53.75   $53.70  
  Purchase #3 $149.49   5.159%   $157.2022   $157.20   $157.20   $157.20  
  Purchase #4 $115.82   7.680%   $124.715   $124.72   $124.70   $124.70  
  Purchase #5 $228.97   6.108%   $242.9555   $242.96   $242.95   $243.00  
  Purchase #6 $222.74   6.111%   $236.3516   $236.35   $236.35   $236.40  
  Purchase #7 $104.30   9.637%   $114.3514   $114.35   $114.35   $114.40  
  7 purchase totals = $930.93       $995.9033   $995.91   $995.90   $996.00