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 $25.36   3.706%   $26.2998   $26.30   $26.30   $26.30  
  Purchase #2 $95.68   8.439%   $103.7544   $103.75   $103.75   $103.80  
  Purchase #3 $213.55   6.316%   $227.0378   $227.04   $227.05   $227.00  
  Purchase #4 $238.67   10.148%   $262.8902   $262.89   $262.90   $262.90  
  Purchase #5 $196.46   9.522%   $215.1669   $215.17   $215.15   $215.20  
  Purchase #6 $143.34   6.177%   $152.1941   $152.19   $152.20   $152.20  
  Purchase #7 $240.73   3.864%   $250.0318   $250.03   $250.05   $250.00  
  7 purchase totals = $1,153.79       $1,237.3750   $1,237.37   $1,237.40   $1,237.40