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	$71.49	9.821%	$78.511	$78.51	$78.50	$78.50
Purchase #2	$190.33	3.437%	$196.8716	$196.87	$196.85	$196.90
Purchase #3	$187.37	11.639%	$209.178	$209.18	$209.20	$209.20
Purchase #4	$183.80	5.622%	$194.1332	$194.13	$194.15	$194.10
Purchase #5	$10.31	7.282%	$11.0608	$11.06	$11.05	$11.10
Purchase #6	$60.95	7.298%	$65.3981	$65.40	$65.40	$65.40
Purchase #7	$237.71	9.565%	$260.447	$260.45	$260.45	$260.40
7 purchase totals =	$941.96		$1,015.5997	$1,015.60	$1,015.60	$1,015.60