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	$164.99	6.300%	$175.3844	$175.38	$175.40	$175.40
Purchase #2	$128.90	4.599%	$134.8281	$134.83	$134.85	$134.80
Purchase #3	$195.47	7.463%	$210.0579	$210.06	$210.05	$210.10
Purchase #4	$125.90	13.873%	$143.3661	$143.37	$143.35	$143.40
Purchase #5	$152.31	4.716%	$159.4929	$159.49	$159.50	$159.50
Purchase #6	$71.88	7.247%	$77.0891	$77.09	$77.10	$77.10
Purchase #7	$226.69	12.555%	$255.1509	$255.15	$255.15	$255.20
7 purchase totals =	$1,066.14		$1,155.3694	$1,155.37	$1,155.40	$1,155.50