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	$33.53	9.686%	$36.7777	$36.78	$36.80	$36.80
Purchase #2	$173.30	7.156%	$185.7013	$185.70	$185.70	$185.70
Purchase #3	$146.26	5.534%	$154.354	$154.35	$154.35	$154.40
Purchase #4	$51.83	13.663%	$58.9115	$58.91	$58.90	$58.90
Purchase #5	$54.58	9.108%	$59.5511	$59.55	$59.55	$59.60
Purchase #6	$111.31	6.432%	$118.4695	$118.47	$118.45	$118.50
Purchase #7	$24.32	5.565%	$25.6734	$25.67	$25.65	$25.70
7 purchase totals =	$595.13		$639.4385	$639.43	$639.40	$639.60