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 $136.57   8.239%   $147.822   $147.82   $147.80   $147.80  
  Purchase #2 $103.54   10.762%   $114.683   $114.68   $114.70   $114.70  
  Purchase #3 $180.70   3.314%   $186.6884   $186.69   $186.70   $186.70  
  Purchase #4 $210.77   4.796%   $220.8785   $220.88   $220.90   $220.90  
  Purchase #5 $239.41   5.339%   $252.1921   $252.19   $252.20   $252.20  
  Purchase #6 $119.86   3.662%   $124.2493   $124.25   $124.25   $124.20  
  Purchase #7 $168.44   11.569%   $187.9268   $187.93   $187.95   $187.90  
  7 purchase totals = $1,159.29       $1,234.4401   $1,234.44   $1,234.50   $1,234.40