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 $244.84   4.839%   $256.6878   $256.69   $256.70   $256.70  
  Purchase #2 $134.86   13.848%   $153.5354   $153.54   $153.55   $153.50  
  Purchase #3 $24.56   7.493%   $26.4003   $26.40   $26.40   $26.40  
  Purchase #4 $42.73   10.566%   $47.2449   $47.24   $47.25   $47.20  
  Purchase #5 $224.86   5.234%   $236.6292   $236.63   $236.65   $236.60  
  Purchase #6 $178.35   3.768%   $185.0702   $185.07   $185.05   $185.10  
  Purchase #7 $125.68   11.732%   $140.4248   $140.42   $140.40   $140.40  
  7 purchase totals = $975.88       $1,045.9926   $1,045.99   $1,046.00   $1,045.90