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	$138.86	6.439%	$147.8012	$147.80	$147.80	$147.80
Purchase #2	$97.29	8.680%	$105.7348	$105.73	$105.75	$105.70
Purchase #3	$70.95	10.663%	$78.5154	$78.52	$78.50	$78.50
Purchase #4	$214.44	12.576%	$241.408	$241.41	$241.40	$241.40
Purchase #5	$143.95	9.841%	$158.1161	$158.12	$158.10	$158.10
Purchase #6	$42.91	8.169%	$46.4153	$46.42	$46.40	$46.40
Purchase #7	$248.76	6.395%	$264.6682	$264.67	$264.65	$264.70
7 purchase totals =	$957.16		$1,042.6590	$1,042.67	$1,042.60	$1,042.60