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 $241.83   13.418%   $274.2787   $274.28   $274.30   $274.30  
  Purchase #2 $156.51   5.340%   $164.8676   $164.87   $164.85   $164.90  
  Purchase #3 $118.84   5.762%   $125.6876   $125.69   $125.70   $125.70  
  Purchase #4 $235.95   6.789%   $251.9686   $251.97   $251.95   $252.00  
  Purchase #5 $242.64   12.709%   $273.4771   $273.48   $273.50   $273.50  
  Purchase #6 $227.73   13.253%   $257.9111   $257.91   $257.90   $257.90  
  Purchase #7 $163.41   12.714%   $184.1859   $184.19   $184.20   $184.20  
  7 purchase totals = $1,386.91       $1,532.3766   $1,532.39   $1,532.40   $1,532.50