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 $245.46   6.728%   $261.9745   $261.97   $261.95   $262.00  
  Purchase #2 $201.32   3.694%   $208.7568   $208.76   $208.75   $208.80  
  Purchase #3 $178.37   8.439%   $193.4226   $193.42   $193.40   $193.40  
  Purchase #4 $119.78   13.399%   $135.8293   $135.83   $135.85   $135.80  
  Purchase #5 $156.92   10.481%   $173.3668   $173.37   $173.35   $173.40  
  Purchase #6 $212.76   10.304%   $234.6828   $234.68   $234.70   $234.70  
  Purchase #7 $205.30   6.142%   $217.9095   $217.91   $217.90   $217.90  
  7 purchase totals = $1,319.91       $1,425.9423   $1,425.94   $1,425.90   $1,426.00