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 $242.87   12.808%   $273.9768   $273.98   $274.00   $274.00  
  Purchase #2 $195.61   9.762%   $214.7054   $214.71   $214.70   $214.70  
  Purchase #3 $76.37   11.150%   $84.8853   $84.89   $84.90   $84.90  
  Purchase #4 $92.90   5.413%   $97.9287   $97.93   $97.95   $97.90  
  Purchase #5 $209.75   3.596%   $217.2926   $217.29   $217.30   $217.30  
  Purchase #6 $101.37   5.330%   $106.773   $106.77   $106.75   $106.80  
  Purchase #7 $240.86   8.547%   $261.4463   $261.45   $261.45   $261.40  
  7 purchase totals = $1,159.73       $1,257.0081   $1,257.02   $1,257.05   $1,257.00