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 $64.89   4.747%   $67.9703   $67.97   $67.95   $68.00  
  Purchase #2 $158.59   3.840%   $164.6799   $164.68   $164.70   $164.70  
  Purchase #3 $115.80   12.184%   $129.9091   $129.91   $129.90   $129.90  
  Purchase #4 $51.94   4.611%   $54.335   $54.34   $54.35   $54.30  
  Purchase #5 $74.61   5.669%   $78.8396   $78.84   $78.85   $78.80  
  Purchase #6 $220.48   13.244%   $249.6804   $249.68   $249.70   $249.70  
  Purchase #7 $211.40   13.298%   $239.512   $239.51   $239.50   $239.50  
  7 purchase totals = $897.71       $984.9263   $984.93   $984.95   $984.90