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 $240.99   8.410%   $261.2573   $261.26   $261.25   $261.30  
  Purchase #2 $81.27   4.772%   $85.1482   $85.15   $85.15   $85.10  
  Purchase #3 $176.70   10.146%   $194.628   $194.63   $194.65   $194.60  
  Purchase #4 $166.76   5.691%   $176.2503   $176.25   $176.25   $176.30  
  Purchase #5 $231.80   10.873%   $257.0036   $257.00   $257.00   $257.00  
  Purchase #6 $97.98   5.803%   $103.6658   $103.67   $103.65   $103.70  
  Purchase #7 $118.45   5.738%   $125.2467   $125.25   $125.25   $125.20  
  7 purchase totals = $1,113.95       $1,203.1999   $1,203.21   $1,203.20   $1,203.20