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	$55.45	11.650%	$61.9099	$61.91	$61.90	$61.90
Purchase #2	$51.42	9.646%	$56.38	$56.38	$56.40	$56.40
Purchase #3	$153.44	13.195%	$173.6864	$173.69	$173.70	$173.70
Purchase #4	$107.86	7.223%	$115.6507	$115.65	$115.65	$115.70
Purchase #5	$114.90	10.838%	$127.3529	$127.35	$127.35	$127.40
Purchase #6	$198.56	11.559%	$221.5116	$221.51	$221.50	$221.50
Purchase #7	$167.66	4.255%	$174.7939	$174.79	$174.80	$174.80
7 purchase totals =	$849.29		$931.2854	$931.28	$931.30	$931.40