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 $106.55   6.647%   $113.6324   $113.63   $113.65   $113.60  
  Purchase #2 $14.93   8.203%   $16.1547   $16.15   $16.15   $16.20  
  Purchase #3 $104.40   9.808%   $114.6396   $114.64   $114.65   $114.60  
  Purchase #4 $114.53   13.669%   $130.1851   $130.19   $130.20   $130.20  
  Purchase #5 $172.25   3.361%   $178.0393   $178.04   $178.05   $178.00  
  Purchase #6 $121.33   5.443%   $127.934   $127.93   $127.95   $127.90  
  Purchase #7 $41.44   6.315%   $44.0569   $44.06   $44.05   $44.10  
  7 purchase totals = $675.43       $724.6420   $724.64   $724.70   $724.60