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	$127.84	7.557%	$137.5009	$137.50	$137.50	$137.50
Purchase #2	$106.75	4.586%	$111.6456	$111.65	$111.65	$111.60
Purchase #3	$36.95	5.375%	$38.9361	$38.94	$38.95	$38.90
Purchase #4	$42.27	9.720%	$46.3786	$46.38	$46.40	$46.40
Purchase #5	$67.52	11.137%	$75.0397	$75.04	$75.05	$75.00
Purchase #6	$212.65	8.245%	$230.183	$230.18	$230.20	$230.20
Purchase #7	$24.74	11.117%	$27.4903	$27.49	$27.50	$27.50
7 purchase totals =	$618.72		$667.1742	$667.18	$667.25	$667.10