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 $213.30   13.806%   $242.7482   $242.75   $242.75   $242.70  
  Purchase #2 $122.78   8.862%   $133.6608   $133.66   $133.65   $133.70  
  Purchase #3 $190.73   4.104%   $198.5576   $198.56   $198.55   $198.60  
  Purchase #4 $220.42   12.527%   $248.032   $248.03   $248.05   $248.00  
  Purchase #5 $31.90   7.563%   $34.3126   $34.31   $34.30   $34.30  
  Purchase #6 $151.80   10.387%   $167.5675   $167.57   $167.55   $167.60  
  Purchase #7 $220.98   4.326%   $230.5396   $230.54   $230.55   $230.50  
  7 purchase totals = $1,151.91       $1,255.4183   $1,255.42   $1,255.40   $1,255.40