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	$166.81	7.771%	$179.7728	$179.77	$179.75	$179.80
Purchase #2	$117.31	11.734%	$131.0752	$131.08	$131.10	$131.10
Purchase #3	$120.72	6.669%	$128.7708	$128.77	$128.75	$128.80
Purchase #4	$50.38	12.433%	$56.6437	$56.64	$56.65	$56.60
Purchase #5	$211.99	8.265%	$229.511	$229.51	$229.50	$229.50
Purchase #6	$49.31	4.258%	$51.4096	$51.41	$51.40	$51.40
Purchase #7	$130.58	5.184%	$137.3493	$137.35	$137.35	$137.30
7 purchase totals =	$847.10		$914.5324	$914.53	$914.50	$914.50