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 $241.91   9.830%   $265.6898   $265.69   $265.70   $265.70  
  Purchase #2 $188.50   4.770%   $197.4915   $197.49   $197.50   $197.50  
  Purchase #3 $53.84   8.780%   $58.5672   $58.57   $58.55   $58.60  
  Purchase #4 $223.36   10.542%   $246.9066   $246.91   $246.90   $246.90  
  Purchase #5 $226.44   9.461%   $247.8635   $247.86   $247.85   $247.90  
  Purchase #6 $250.69   10.862%   $277.9199   $277.92   $277.90   $277.90  
  Purchase #7 $180.71   10.388%   $199.4822   $199.48   $199.50   $199.50  
  7 purchase totals = $1,365.45       $1,493.9207   $1,493.92   $1,493.90   $1,494.00