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 $85.69   11.650%   $95.6729   $95.67   $95.65   $95.70  
  Purchase #2 $164.85   13.615%   $187.2943   $187.29   $187.30   $187.30  
  Purchase #3 $206.55   10.160%   $227.5355   $227.54   $227.55   $227.50  
  Purchase #4 $232.86   12.182%   $261.227   $261.23   $261.25   $261.20  
  Purchase #5 $67.41   6.352%   $71.6919   $71.69   $71.70   $71.70  
  Purchase #6 $27.93   13.361%   $31.6617   $31.66   $31.65   $31.70  
  Purchase #7 $90.81   12.255%   $101.9388   $101.94   $101.95   $101.90  
  7 purchase totals = $876.10       $977.0221   $977.02   $977.05   $977.00