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 $60.89   4.116%   $63.3962   $63.40   $63.40   $63.40  
  Purchase #2 $123.35   8.342%   $133.6399   $133.64   $133.65   $133.60  
  Purchase #3 $38.49   10.797%   $42.6458   $42.65   $42.65   $42.60  
  Purchase #4 $218.34   8.295%   $236.4513   $236.45   $236.45   $236.50  
  Purchase #5 $81.46   12.228%   $91.4209   $91.42   $91.40   $91.40  
  Purchase #6 $162.94   9.151%   $177.8506   $177.85   $177.85   $177.90  
  Purchase #7 $111.36   5.293%   $117.2543   $117.25   $117.25   $117.30  
  7 purchase totals = $796.83       $862.6590   $862.66   $862.65   $862.70