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 $86.84   12.679%   $97.8504   $97.85   $97.85   $97.90  
  Purchase #2 $248.29   5.292%   $261.4295   $261.43   $261.45   $261.40  
  Purchase #3 $17.87   9.158%   $19.5065   $19.51   $19.50   $19.50  
  Purchase #4 $95.29   3.122%   $98.265   $98.27   $98.25   $98.30  
  Purchase #5 $159.54   8.169%   $172.5728   $172.57   $172.55   $172.60  
  Purchase #6 $245.46   13.106%   $277.63   $277.63   $277.65   $277.60  
  Purchase #7 $91.95   9.440%   $100.6301   $100.63   $100.65   $100.60  
  7 purchase totals = $945.24       $1,027.8843   $1,027.89   $1,027.90   $1,027.90