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 $117.84   5.541%   $124.3695   $124.37   $124.35   $124.40  
  Purchase #2 $197.65   9.156%   $215.7468   $215.75   $215.75   $215.70  
  Purchase #3 $228.63   10.302%   $252.1835   $252.18   $252.20   $252.20  
  Purchase #4 $92.57   5.749%   $97.8918   $97.89   $97.90   $97.90  
  Purchase #5 $250.36   4.623%   $261.9341   $261.93   $261.95   $261.90  
  Purchase #6 $92.54   5.424%   $97.5594   $97.56   $97.55   $97.60  
  Purchase #7 $11.82   10.710%   $13.0859   $13.09   $13.10   $13.10  
  7 purchase totals = $991.41       $1,062.7710   $1,062.77   $1,062.80   $1,062.80