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 $59.78   11.316%   $66.5447   $66.54   $66.55   $66.50  
  Purchase #2 $122.64   6.826%   $131.0114   $131.01   $131.00   $131.00  
  Purchase #3 $239.66   9.127%   $261.5338   $261.53   $261.55   $261.50  
  Purchase #4 $42.64   5.558%   $45.0099   $45.01   $45.00   $45.00  
  Purchase #5 $109.30   5.432%   $115.2372   $115.24   $115.25   $115.20  
  Purchase #6 $192.35   5.467%   $202.8658   $202.87   $202.85   $202.90  
  Purchase #7 $240.29   5.287%   $252.9941   $252.99   $253.00   $253.00  
  7 purchase totals = $1,006.66       $1,075.1969   $1,075.19   $1,075.20   $1,075.10