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	$112.72	10.123%	$124.1306	$124.13	$124.15	$124.10
Purchase #2	$193.53	5.639%	$204.4432	$204.44	$204.45	$204.40
Purchase #3	$211.88	8.762%	$230.4449	$230.44	$230.45	$230.40
Purchase #4	$103.97	7.395%	$111.6586	$111.66	$111.65	$111.70
Purchase #5	$204.69	3.341%	$211.5287	$211.53	$211.55	$211.50
Purchase #6	$56.63	5.194%	$59.5714	$59.57	$59.55	$59.60
Purchase #7	$45.60	11.558%	$50.8704	$50.87	$50.85	$50.90
7 purchase totals =	$929.02		$992.6478	$992.64	$992.65	$992.60