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	$10.64	10.762%	$11.7851	$11.79	$11.80	$11.80
Purchase #2	$53.66	9.379%	$58.6928	$58.69	$58.70	$58.70
Purchase #3	$44.28	5.211%	$46.5874	$46.59	$46.60	$46.60
Purchase #4	$223.85	13.110%	$253.1967	$253.20	$253.20	$253.20
Purchase #5	$103.71	7.839%	$111.8398	$111.84	$111.85	$111.80
Purchase #6	$67.83	13.777%	$77.1749	$77.17	$77.15	$77.20
Purchase #7	$82.51	4.842%	$86.5051	$86.51	$86.50	$86.50
7 purchase totals =	$586.48		$645.7818	$645.79	$645.80	$645.80