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 $32.46   7.212%   $34.801   $34.80   $34.80   $34.80  
  Purchase #2 $244.46   6.651%   $260.719   $260.72   $260.70   $260.70  
  Purchase #3 $115.88   3.314%   $119.7203   $119.72   $119.70   $119.70  
  Purchase #4 $165.76   4.420%   $173.0866   $173.09   $173.10   $173.10  
  Purchase #5 $189.77   3.761%   $196.9072   $196.91   $196.90   $196.90  
  Purchase #6 $217.85   8.187%   $235.6854   $235.69   $235.70   $235.70  
  Purchase #7 $205.46   10.390%   $226.8073   $226.81   $226.80   $226.80  
  7 purchase totals = $1,171.64       $1,247.7268   $1,247.74   $1,247.70   $1,247.70