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 $184.97   11.660%   $206.5375   $206.54   $206.55   $206.50  
  Purchase #2 $229.90   7.290%   $246.6597   $246.66   $246.65   $246.70  
  Purchase #3 $81.76   5.667%   $86.3933   $86.39   $86.40   $86.40  
  Purchase #4 $126.69   3.287%   $130.8543   $130.85   $130.85   $130.90  
  Purchase #5 $30.65   8.122%   $33.1394   $33.14   $33.15   $33.10  
  Purchase #6 $213.93   8.383%   $231.8638   $231.86   $231.85   $231.90  
  Purchase #7 $222.86   13.184%   $252.2419   $252.24   $252.25   $252.20  
  7 purchase totals = $1,090.76       $1,187.6899   $1,187.68   $1,187.70   $1,187.70