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	$111.60	3.588%	$115.6042	$115.60	$115.60	$115.60
Purchase #2	$101.91	10.288%	$112.3945	$112.39	$112.40	$112.40
Purchase #3	$248.32	9.367%	$271.5801	$271.58	$271.60	$271.60
Purchase #4	$62.90	13.653%	$71.4877	$71.49	$71.50	$71.50
Purchase #5	$73.74	5.656%	$77.9107	$77.91	$77.90	$77.90
Purchase #6	$221.99	3.733%	$230.2769	$230.28	$230.30	$230.30
Purchase #7	$127.36	7.258%	$136.6038	$136.60	$136.60	$136.60
7 purchase totals =	$947.82		$1,015.8579	$1,015.85	$1,015.90	$1,015.90