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	$49.72	6.142%	$52.7738	$52.77	$52.75	$52.80
Purchase #2	$13.69	9.830%	$15.0357	$15.04	$15.05	$15.00
Purchase #3	$11.91	5.549%	$12.5709	$12.57	$12.55	$12.60
Purchase #4	$248.56	4.217%	$259.0418	$259.04	$259.05	$259.00
Purchase #5	$116.73	9.137%	$127.3956	$127.40	$127.40	$127.40
Purchase #6	$97.92	5.271%	$103.0814	$103.08	$103.10	$103.10
Purchase #7	$67.31	3.342%	$69.5595	$69.56	$69.55	$69.60
7 purchase totals =	$605.84		$639.4587	$639.46	$639.45	$639.50