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	$99.31	9.685%	$108.9282	$108.93	$108.95	$108.90
Purchase #2	$67.60	5.553%	$71.3538	$71.35	$71.35	$71.40
Purchase #3	$55.67	11.379%	$62.0047	$62.00	$62.00	$62.00
Purchase #4	$101.70	9.367%	$111.2262	$111.23	$111.25	$111.20
Purchase #5	$117.73	9.303%	$128.6824	$128.68	$128.70	$128.70
Purchase #6	$192.34	9.227%	$210.0872	$210.09	$210.10	$210.10
Purchase #7	$19.36	10.672%	$21.4261	$21.43	$21.45	$21.40
7 purchase totals =	$653.71		$713.7086	$713.71	$713.80	$713.70