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	$19.32	11.123%	$21.469	$21.47	$21.45	$21.50
Purchase #2	$91.27	12.523%	$102.6997	$102.70	$102.70	$102.70
Purchase #3	$230.59	3.747%	$239.2302	$239.23	$239.25	$239.20
Purchase #4	$147.48	4.209%	$153.6874	$153.69	$153.70	$153.70
Purchase #5	$108.86	13.757%	$123.8359	$123.84	$123.85	$123.80
Purchase #6	$35.55	11.435%	$39.6151	$39.62	$39.60	$39.60
Purchase #7	$208.89	6.739%	$222.9671	$222.97	$222.95	$223.00
7 purchase totals =	$841.96		$903.5044	$903.52	$903.50	$903.50