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 $60.86   6.157%   $64.6072   $64.61   $64.60   $64.60  
  Purchase #2 $190.82   6.231%   $202.71   $202.71   $202.70   $202.70  
  Purchase #3 $18.28   3.552%   $18.9293   $18.93   $18.95   $18.90  
  Purchase #4 $109.72   8.649%   $119.2097   $119.21   $119.20   $119.20  
  Purchase #5 $67.65   4.299%   $70.5583   $70.56   $70.55   $70.60  
  Purchase #6 $105.39   8.743%   $114.6042   $114.60   $114.60   $114.60  
  Purchase #7 $73.79   11.263%   $82.101   $82.10   $82.10   $82.10  
  7 purchase totals = $626.51       $672.7197   $672.72   $672.70   $672.70