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 $214.68   11.714%   $239.8276   $239.83   $239.85   $239.80  
  Purchase #2 $212.93   9.450%   $233.0519   $233.05   $233.05   $233.10  
  Purchase #3 $114.46   9.489%   $125.3211   $125.32   $125.30   $125.30  
  Purchase #4 $71.41   6.772%   $76.2459   $76.25   $76.25   $76.20  
  Purchase #5 $80.99   11.782%   $90.5322   $90.53   $90.55   $90.50  
  Purchase #6 $216.95   4.165%   $225.986   $225.99   $226.00   $226.00  
  Purchase #7 $216.36   5.183%   $227.5739   $227.57   $227.55   $227.60  
  7 purchase totals = $1,127.78       $1,218.5386   $1,218.54   $1,218.55   $1,218.50