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 $59.65   11.618%   $66.5801   $66.58   $66.60   $66.60  
  Purchase #2 $157.83   12.273%   $177.2005   $177.20   $177.20   $177.20  
  Purchase #3 $205.89   4.308%   $214.7597   $214.76   $214.75   $214.80  
  Purchase #4 $220.43   4.769%   $230.9423   $230.94   $230.95   $230.90  
  Purchase #5 $21.67   10.439%   $23.9321   $23.93   $23.95   $23.90  
  Purchase #6 $208.44   8.684%   $226.5409   $226.54   $226.55   $226.50  
  Purchase #7 $206.42   13.702%   $234.7037   $234.70   $234.70   $234.70  
  7 purchase totals = $1,080.33       $1,174.6593   $1,174.65   $1,174.70   $1,174.60