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 $109.63   9.193%   $119.7083   $119.71   $119.70   $119.70  
  Purchase #2 $228.56   6.272%   $242.8953   $242.90   $242.90   $242.90  
  Purchase #3 $13.49   8.182%   $14.5938   $14.59   $14.60   $14.60  
  Purchase #4 $141.91   11.243%   $157.8649   $157.86   $157.85   $157.90  
  Purchase #5 $198.32   3.209%   $204.6841   $204.68   $204.70   $204.70  
  Purchase #6 $247.87   7.268%   $265.8852   $265.89   $265.90   $265.90  
  Purchase #7 $216.68   4.347%   $226.0991   $226.10   $226.10   $226.10  
  7 purchase totals = $1,156.46       $1,231.7307   $1,231.73   $1,231.75   $1,231.80