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 $23.50   13.791%   $26.7409   $26.74   $26.75   $26.70  
  Purchase #2 $97.31   8.489%   $105.5706   $105.57   $105.55   $105.60  
  Purchase #3 $41.88   13.843%   $47.6774   $47.68   $47.70   $47.70  
  Purchase #4 $95.93   13.499%   $108.8796   $108.88   $108.90   $108.90  
  Purchase #5 $98.82   5.299%   $104.0565   $104.06   $104.05   $104.10  
  Purchase #6 $49.32   13.194%   $55.8273   $55.83   $55.85   $55.80  
  Purchase #7 $110.99   4.769%   $116.2831   $116.28   $116.30   $116.30  
  7 purchase totals = $517.75       $565.0354   $565.04   $565.10   $565.10