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 $68.58   13.209%   $77.6387   $77.64   $77.65   $77.60  
  Purchase #2 $183.66   4.762%   $192.4059   $192.41   $192.40   $192.40  
  Purchase #3 $101.26   6.348%   $107.688   $107.69   $107.70   $107.70  
  Purchase #4 $250.33   8.499%   $271.6055   $271.61   $271.60   $271.60  
  Purchase #5 $125.37   6.195%   $133.1367   $133.14   $133.15   $133.10  
  Purchase #6 $31.39   9.750%   $34.4505   $34.45   $34.45   $34.50  
  Purchase #7 $198.86   13.636%   $225.9765   $225.98   $226.00   $226.00  
  7 purchase totals = $959.45       $1,042.9018   $1,042.92   $1,042.95   $1,042.90