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	$85.37	5.456%	$90.0278	$90.03	$90.05	$90.00
Purchase #2	$120.87	13.827%	$137.5827	$137.58	$137.60	$137.60
Purchase #3	$108.51	9.224%	$118.519	$118.52	$118.50	$118.50
Purchase #4	$190.62	10.422%	$210.4864	$210.49	$210.50	$210.50
Purchase #5	$128.59	12.497%	$144.6599	$144.66	$144.65	$144.70
Purchase #6	$211.41	12.560%	$237.9631	$237.96	$237.95	$238.00
Purchase #7	$197.74	3.735%	$205.1256	$205.13	$205.15	$205.10
7 purchase totals =	$1,043.11		$1,144.3645	$1,144.37	$1,144.40	$1,144.40