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 $30.81   13.387%   $34.9345   $34.93   $34.95   $34.90  
  Purchase #2 $84.55   11.795%   $94.5227   $94.52   $94.50   $94.50  
  Purchase #3 $241.78   10.296%   $266.6737   $266.67   $266.65   $266.70  
  Purchase #4 $67.58   8.515%   $73.3344   $73.33   $73.35   $73.30  
  Purchase #5 $90.92   4.344%   $94.8696   $94.87   $94.85   $94.90  
  Purchase #6 $174.66   5.151%   $183.6567   $183.66   $183.65   $183.70  
  Purchase #7 $207.63   3.186%   $214.2451   $214.25   $214.25   $214.20  
  7 purchase totals = $897.93       $962.2367   $962.23   $962.20   $962.20