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 $233.25   11.376%   $259.7845   $259.78   $259.80   $259.80  
  Purchase #2 $226.42   4.108%   $235.7213   $235.72   $235.70   $235.70  
  Purchase #3 $50.81   10.204%   $55.9947   $55.99   $56.00   $56.00  
  Purchase #4 $204.51   11.233%   $227.4826   $227.48   $227.50   $227.50  
  Purchase #5 $69.41   3.692%   $71.9726   $71.97   $71.95   $72.00  
  Purchase #6 $240.28   10.513%   $265.5406   $265.54   $265.55   $265.50  
  Purchase #7 $192.43   5.452%   $202.9213   $202.92   $202.90   $202.90  
  7 purchase totals = $1,217.11       $1,319.4176   $1,319.40   $1,319.40   $1,319.40