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 $60.25   10.577%   $66.6226   $66.62   $66.60   $66.60  
  Purchase #2 $242.33   11.213%   $269.5025   $269.50   $269.50   $269.50  
  Purchase #3 $34.68   12.156%   $38.8957   $38.90   $38.90   $38.90  
  Purchase #4 $46.28   3.174%   $47.7489   $47.75   $47.75   $47.70  
  Purchase #5 $67.46   11.751%   $75.3872   $75.39   $75.40   $75.40  
  Purchase #6 $72.57   8.591%   $78.8045   $78.80   $78.80   $78.80  
  Purchase #7 $142.64   3.345%   $147.4113   $147.41   $147.40   $147.40  
  7 purchase totals = $666.21       $724.3727   $724.37   $724.35   $724.30