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 $60.90   8.326%   $65.9705   $65.97   $65.95   $66.00  
  Purchase #2 $121.26   4.564%   $126.7943   $126.79   $126.80   $126.80  
  Purchase #3 $99.49   10.254%   $109.6917   $109.69   $109.70   $109.70  
  Purchase #4 $72.67   4.716%   $76.0971   $76.10   $76.10   $76.10  
  Purchase #5 $239.82   5.369%   $252.6959   $252.70   $252.70   $252.70  
  Purchase #6 $59.95   11.473%   $66.8281   $66.83   $66.85   $66.80  
  Purchase #7 $28.71   3.326%   $29.6649   $29.66   $29.65   $29.70  
  7 purchase totals = $682.80       $727.7425   $727.74   $727.75   $727.80