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 $92.34   6.794%   $98.6136   $98.61   $98.60   $98.60  
  Purchase #2 $180.62   3.754%   $187.4005   $187.40   $187.40   $187.40  
  Purchase #3 $234.68   11.457%   $261.5673   $261.57   $261.55   $261.60  
  Purchase #4 $235.70   5.616%   $248.9369   $248.94   $248.95   $248.90  
  Purchase #5 $235.53   8.664%   $255.9363   $255.94   $255.95   $255.90  
  Purchase #6 $10.91   12.367%   $12.2592   $12.26   $12.25   $12.30  
  Purchase #7 $176.63   8.330%   $191.3433   $191.34   $191.35   $191.30  
  7 purchase totals = $1,166.41       $1,256.0571   $1,256.06   $1,256.05   $1,256.00