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 $213.76   9.559%   $234.1933   $234.19   $234.20   $234.20  
  Purchase #2 $171.64   7.286%   $184.1457   $184.15   $184.15   $184.10  
  Purchase #3 $16.32   8.125%   $17.646   $17.65   $17.65   $17.60  
  Purchase #4 $139.56   12.581%   $157.118   $157.12   $157.10   $157.10  
  Purchase #5 $21.56   10.122%   $23.7423   $23.74   $23.75   $23.70  
  Purchase #6 $61.61   3.369%   $63.6856   $63.69   $63.70   $63.70  
  Purchase #7 $58.51   9.668%   $64.1667   $64.17   $64.15   $64.20  
  7 purchase totals = $682.96       $744.6976   $744.71   $744.70   $744.60