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 $226.43   6.692%   $241.5827   $241.58   $241.60   $241.60  
  Purchase #2 $130.66   4.806%   $136.9395   $136.94   $136.95   $136.90  
  Purchase #3 $115.53   8.866%   $125.7729   $125.77   $125.75   $125.80  
  Purchase #4 $247.40   4.115%   $257.5805   $257.58   $257.60   $257.60  
  Purchase #5 $190.85   12.702%   $215.0918   $215.09   $215.10   $215.10  
  Purchase #6 $121.97   12.724%   $137.4895   $137.49   $137.50   $137.50  
  Purchase #7 $146.97   6.274%   $156.1909   $156.19   $156.20   $156.20  
  7 purchase totals = $1,179.81       $1,270.6478   $1,270.64   $1,270.70   $1,270.70