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	$18.29	12.733%	$20.6189	$20.62	$20.60	$20.60
Purchase #2	$43.91	3.623%	$45.5009	$45.50	$45.50	$45.50
Purchase #3	$105.26	8.449%	$114.1534	$114.15	$114.15	$114.20
Purchase #4	$139.66	12.239%	$156.753	$156.75	$156.75	$156.80
Purchase #5	$217.63	5.498%	$229.5953	$229.60	$229.60	$229.60
Purchase #6	$35.27	8.457%	$38.2528	$38.25	$38.25	$38.30
Purchase #7	$35.95	13.156%	$40.6796	$40.68	$40.70	$40.70
7 purchase totals =	$595.97		$645.5539	$645.55	$645.55	$645.70