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 $211.73   6.407%   $225.2955   $225.30   $225.30   $225.30  
  Purchase #2 $232.27   10.780%   $257.3087   $257.31   $257.30   $257.30  
  Purchase #3 $197.90   5.567%   $208.9171   $208.92   $208.90   $208.90  
  Purchase #4 $68.87   10.744%   $76.2694   $76.27   $76.25   $76.30  
  Purchase #5 $119.87   4.536%   $125.3073   $125.31   $125.30   $125.30  
  Purchase #6 $174.76   12.395%   $196.4215   $196.42   $196.40   $196.40  
  Purchase #7 $162.41   9.115%   $177.2137   $177.21   $177.20   $177.20  
  7 purchase totals = $1,167.81       $1,266.7332   $1,266.74   $1,266.65   $1,266.70