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	$139.38	3.869%	$144.7726	$144.77	$144.75	$144.80
Purchase #2	$40.40	12.205%	$45.3308	$45.33	$45.35	$45.30
Purchase #3	$10.90	5.388%	$11.4873	$11.49	$11.50	$11.50
Purchase #4	$111.60	9.774%	$122.5078	$122.51	$122.50	$122.50
Purchase #5	$49.39	8.359%	$53.5185	$53.52	$53.50	$53.50
Purchase #6	$38.87	11.240%	$43.239	$43.24	$43.25	$43.20
Purchase #7	$92.97	7.406%	$99.8554	$99.86	$99.85	$99.90
7 purchase totals =	$483.51		$520.7114	$520.72	$520.70	$520.70