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 $248.39   5.407%   $261.8204   $261.82   $261.80   $261.80  
  Purchase #2 $21.71   8.712%   $23.6014   $23.60   $23.60   $23.60  
  Purchase #3 $76.74   6.293%   $81.5692   $81.57   $81.55   $81.60  
  Purchase #4 $112.31   12.103%   $125.9029   $125.90   $125.90   $125.90  
  Purchase #5 $124.51   8.754%   $135.4096   $135.41   $135.40   $135.40  
  Purchase #6 $65.88   13.371%   $74.6888   $74.69   $74.70   $74.70  
  Purchase #7 $184.45   3.867%   $191.5827   $191.58   $191.60   $191.60  
  7 purchase totals = $833.99       $894.5750   $894.57   $894.55   $894.60