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 $98.53   13.853%   $112.1794   $112.18   $112.20   $112.20  
  Purchase #2 $119.56   6.565%   $127.4091   $127.41   $127.40   $127.40  
  Purchase #3 $236.32   3.776%   $245.2434   $245.24   $245.25   $245.20  
  Purchase #4 $48.55   10.137%   $53.4715   $53.47   $53.45   $53.50  
  Purchase #5 $151.48   13.347%   $171.698   $171.70   $171.70   $171.70  
  Purchase #6 $143.76   9.124%   $156.8767   $156.88   $156.90   $156.90  
  Purchase #7 $186.77   8.713%   $203.0433   $203.04   $203.05   $203.00  
  7 purchase totals = $984.97       $1,069.9214   $1,069.92   $1,069.95   $1,069.90