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	$132.99	13.663%	$151.1604	$151.16	$151.15	$151.20
Purchase #2	$250.71	6.293%	$266.4872	$266.49	$266.50	$266.50
Purchase #3	$221.71	12.361%	$249.1156	$249.12	$249.10	$249.10
Purchase #4	$19.76	5.630%	$20.8725	$20.87	$20.85	$20.90
Purchase #5	$54.25	12.711%	$61.1457	$61.15	$61.15	$61.10
Purchase #6	$79.95	3.414%	$82.6795	$82.68	$82.70	$82.70
Purchase #7	$10.73	11.415%	$11.9548	$11.95	$11.95	$12.00
7 purchase totals =	$770.10		$843.4157	$843.42	$843.40	$843.50