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 $232.93   13.208%   $263.6954   $263.70   $263.70   $263.70  
  Purchase #2 $14.90   3.498%   $15.4212   $15.42   $15.40   $15.40  
  Purchase #3 $207.89   9.544%   $227.731   $227.73   $227.75   $227.70  
  Purchase #4 $107.36   7.366%   $115.2681   $115.27   $115.25   $115.30  
  Purchase #5 $241.98   9.572%   $265.1423   $265.14   $265.15   $265.10  
  Purchase #6 $112.75   13.170%   $127.5992   $127.60   $127.60   $127.60  
  Purchase #7 $242.64   5.637%   $256.3176   $256.32   $256.30   $256.30  
  7 purchase totals = $1,160.45       $1,271.1748   $1,271.18   $1,271.15   $1,271.10