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	$217.74	12.298%	$244.5177	$244.52	$244.50	$244.50
Purchase #2	$92.43	6.269%	$98.2244	$98.22	$98.20	$98.20
Purchase #3	$58.59	11.145%	$65.1199	$65.12	$65.10	$65.10
Purchase #4	$99.82	4.493%	$104.3049	$104.30	$104.30	$104.30
Purchase #5	$233.76	9.433%	$255.8106	$255.81	$255.80	$255.80
Purchase #6	$34.29	11.381%	$38.1925	$38.19	$38.20	$38.20
Purchase #7	$20.88	8.178%	$22.5876	$22.59	$22.60	$22.60
7 purchase totals =	$757.51		$828.7576	$828.75	$828.70	$828.70