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 $61.40   6.107%   $65.1497   $65.15   $65.15   $65.10  
  Purchase #2 $190.85   13.342%   $216.3132   $216.31   $216.30   $216.30  
  Purchase #3 $249.78   9.494%   $273.4941   $273.49   $273.50   $273.50  
  Purchase #4 $214.62   9.316%   $234.614   $234.61   $234.60   $234.60  
  Purchase #5 $118.87   12.617%   $133.8678   $133.87   $133.85   $133.90  
  Purchase #6 $240.32   3.498%   $248.7264   $248.73   $248.75   $248.70  
  Purchase #7 $241.37   10.703%   $267.2038   $267.20   $267.20   $267.20  
  7 purchase totals = $1,317.21       $1,439.3690   $1,439.36   $1,439.35   $1,439.30