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	$175.48	4.815%	$183.9294	$183.93	$183.95	$183.90
Purchase #2	$141.25	3.826%	$146.6542	$146.65	$146.65	$146.70
Purchase #3	$109.41	13.194%	$123.8456	$123.85	$123.85	$123.80
Purchase #4	$85.82	13.178%	$97.1294	$97.13	$97.15	$97.10
Purchase #5	$235.35	10.773%	$260.7043	$260.70	$260.70	$260.70
Purchase #6	$19.28	13.177%	$21.8205	$21.82	$21.80	$21.80
Purchase #7	$53.88	6.734%	$57.5083	$57.51	$57.50	$57.50
7 purchase totals =	$820.47		$891.5917	$891.59	$891.60	$891.50