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 $250.63   5.609%   $264.6878   $264.69   $264.70   $264.70  
  Purchase #2 $157.39   4.242%   $164.0665   $164.07   $164.05   $164.10  
  Purchase #3 $116.48   6.252%   $123.7623   $123.76   $123.75   $123.80  
  Purchase #4 $66.67   8.342%   $72.2316   $72.23   $72.25   $72.20  
  Purchase #5 $86.80   12.562%   $97.7038   $97.70   $97.70   $97.70  
  Purchase #6 $237.62   8.557%   $257.9531   $257.95   $257.95   $258.00  
  Purchase #7 $111.56   13.720%   $126.866   $126.87   $126.85   $126.90  
  7 purchase totals = $1,027.15       $1,107.2711   $1,107.27   $1,107.25   $1,107.40