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 $58.41   11.233%   $64.9712   $64.97   $64.95   $65.00  
  Purchase #2 $24.87   5.214%   $26.1667   $26.17   $26.15   $26.20  
  Purchase #3 $37.48   10.105%   $41.2674   $41.27   $41.25   $41.30  
  Purchase #4 $216.85   6.854%   $231.7129   $231.71   $231.70   $231.70  
  Purchase #5 $196.69   9.259%   $214.9015   $214.90   $214.90   $214.90  
  Purchase #6 $117.90   3.834%   $122.4203   $122.42   $122.40   $122.40  
  Purchase #7 $24.75   3.840%   $25.7004   $25.70   $25.70   $25.70  
  7 purchase totals = $676.95       $727.1404   $727.14   $727.05   $727.20