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 $248.70   7.338%   $266.9496   $266.95   $266.95   $266.90  
  Purchase #2 $199.40   4.437%   $208.2474   $208.25   $208.25   $208.20  
  Purchase #3 $207.95   4.226%   $216.738   $216.74   $216.75   $216.70  
  Purchase #4 $87.71   5.305%   $92.363   $92.36   $92.35   $92.40  
  Purchase #5 $123.43   11.178%   $137.227   $137.23   $137.25   $137.20  
  Purchase #6 $65.31   11.766%   $72.9944   $72.99   $73.00   $73.00  
  Purchase #7 $192.88   3.414%   $199.4649   $199.46   $199.45   $199.50  
  7 purchase totals = $1,125.38       $1,193.9843   $1,193.98   $1,194.00   $1,193.90