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	$238.37	7.365%	$255.926	$255.93	$255.95	$255.90
Purchase #2	$190.88	3.106%	$196.8087	$196.81	$196.80	$196.80
Purchase #3	$101.76	12.164%	$114.1381	$114.14	$114.15	$114.10
Purchase #4	$50.42	8.857%	$54.8857	$54.89	$54.90	$54.90
Purchase #5	$37.45	6.773%	$39.9865	$39.99	$40.00	$40.00
Purchase #6	$79.84	8.615%	$86.7182	$86.72	$86.70	$86.70
Purchase #7	$215.77	10.439%	$238.2942	$238.29	$238.30	$238.30
7 purchase totals =	$914.49		$986.7574	$986.77	$986.80	$986.70