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	$56.28	5.253%	$59.2364	$59.24	$59.25	$59.20
Purchase #2	$158.94	9.445%	$173.9519	$173.95	$173.95	$174.00
Purchase #3	$50.70	11.681%	$56.6223	$56.62	$56.60	$56.60
Purchase #4	$74.93	4.365%	$78.2007	$78.20	$78.20	$78.20
Purchase #5	$151.83	9.314%	$165.9714	$165.97	$165.95	$166.00
Purchase #6	$235.78	5.818%	$249.4977	$249.50	$249.50	$249.50
Purchase #7	$166.99	3.332%	$172.5541	$172.55	$172.55	$172.60
7 purchase totals =	$895.45		$956.0345	$956.03	$956.00	$956.10