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 $93.77   4.117%   $97.6305   $97.63   $97.65   $97.60  
  Purchase #2 $18.99   11.713%   $21.2143   $21.21   $21.20   $21.20  
  Purchase #3 $63.27   11.438%   $70.5068   $70.51   $70.50   $70.50  
  Purchase #4 $69.78   8.157%   $75.472   $75.47   $75.45   $75.50  
  Purchase #5 $153.66   9.482%   $168.23   $168.23   $168.25   $168.20  
  Purchase #6 $246.33   4.497%   $257.4075   $257.41   $257.40   $257.40  
  Purchase #7 $245.38   6.716%   $261.8597   $261.86   $261.85   $261.90  
  7 purchase totals = $891.18       $952.3208   $952.32   $952.30   $952.30