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 $226.26   3.212%   $233.5275   $233.53   $233.55   $233.50  
  Purchase #2 $247.62   9.448%   $271.0151   $271.02   $271.00   $271.00  
  Purchase #3 $14.59   6.426%   $15.5276   $15.53   $15.55   $15.50  
  Purchase #4 $154.95   10.797%   $171.68   $171.68   $171.70   $171.70  
  Purchase #5 $34.40   4.555%   $35.9669   $35.97   $35.95   $36.00  
  Purchase #6 $142.73   13.633%   $162.1884   $162.19   $162.20   $162.20  
  Purchase #7 $116.41   13.230%   $131.811   $131.81   $131.80   $131.80  
  7 purchase totals = $936.96       $1,021.7165   $1,021.73   $1,021.75   $1,021.70