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 $203.25   11.706%   $227.0424   $227.04   $227.05   $227.00  
  Purchase #2 $250.61   13.247%   $283.8083   $283.81   $283.80   $283.80  
  Purchase #3 $22.71   3.447%   $23.4928   $23.49   $23.50   $23.50  
  Purchase #4 $124.99   8.370%   $135.4517   $135.45   $135.45   $135.50  
  Purchase #5 $214.42   11.856%   $239.8416   $239.84   $239.85   $239.80  
  Purchase #6 $208.54   12.508%   $234.6242   $234.62   $234.60   $234.60  
  Purchase #7 $249.76   6.794%   $266.7287   $266.73   $266.75   $266.70  
  7 purchase totals = $1,274.28       $1,410.9897   $1,410.98   $1,411.00   $1,410.90