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 $248.29   7.557%   $267.0533   $267.05   $267.05   $267.10  
  Purchase #2 $79.89   9.777%   $87.7008   $87.70   $87.70   $87.70  
  Purchase #3 $231.76   12.259%   $260.1715   $260.17   $260.15   $260.20  
  Purchase #4 $205.69   10.220%   $226.7115   $226.71   $226.70   $226.70  
  Purchase #5 $30.81   12.729%   $34.7318   $34.73   $34.75   $34.70  
  Purchase #6 $47.41   4.548%   $49.5662   $49.57   $49.55   $49.60  
  Purchase #7 $146.37   7.637%   $157.5483   $157.55   $157.55   $157.50  
  7 purchase totals = $990.22       $1,083.4834   $1,083.48   $1,083.45   $1,083.50