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	$136.84	13.511%	$155.3285	$155.33	$155.35	$155.30
Purchase #2	$149.43	3.709%	$154.9724	$154.97	$154.95	$155.00
Purchase #3	$110.86	4.697%	$116.0671	$116.07	$116.05	$116.10
Purchase #4	$193.60	8.810%	$210.6562	$210.66	$210.65	$210.70
Purchase #5	$118.58	8.269%	$128.3854	$128.39	$128.40	$128.40
Purchase #6	$105.31	6.144%	$111.7802	$111.78	$111.80	$111.80
Purchase #7	$93.60	10.462%	$103.3924	$103.39	$103.40	$103.40
7 purchase totals =	$908.22		$980.5822	$980.59	$980.60	$980.70