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 $239.62   11.856%   $268.0293   $268.03   $268.05   $268.00  
  Purchase #2 $151.39   7.253%   $162.3703   $162.37   $162.35   $162.40  
  Purchase #3 $222.53   4.857%   $233.3383   $233.34   $233.35   $233.30  
  Purchase #4 $196.75   5.253%   $207.0853   $207.09   $207.10   $207.10  
  Purchase #5 $19.64   6.595%   $20.9353   $20.94   $20.95   $20.90  
  Purchase #6 $98.68   8.487%   $107.055   $107.06   $107.05   $107.10  
  Purchase #7 $85.45   7.786%   $92.1031   $92.10   $92.10   $92.10  
  7 purchase totals = $1,014.06       $1,090.9166   $1,090.93   $1,090.95   $1,090.90