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 $176.49   11.530%   $196.8393   $196.84   $196.85   $196.80  
  Purchase #2 $16.88   5.475%   $17.8042   $17.80   $17.80   $17.80  
  Purchase #3 $144.61   11.726%   $161.567   $161.57   $161.55   $161.60  
  Purchase #4 $76.50   6.301%   $81.3203   $81.32   $81.30   $81.30  
  Purchase #5 $119.43   13.414%   $135.4503   $135.45   $135.45   $135.50  
  Purchase #6 $183.26   12.756%   $206.6366   $206.64   $206.65   $206.60  
  Purchase #7 $180.46   3.305%   $186.4242   $186.42   $186.40   $186.40  
  7 purchase totals = $897.63       $986.0419   $986.04   $986.00   $986.00