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	$39.30	7.229%	$42.141	$42.14	$42.15	$42.10
Purchase #2	$124.69	11.461%	$138.9807	$138.98	$139.00	$139.00
Purchase #3	$159.97	6.136%	$169.7858	$169.79	$169.80	$169.80
Purchase #4	$32.25	7.433%	$34.6471	$34.65	$34.65	$34.60
Purchase #5	$214.65	9.721%	$235.5161	$235.52	$235.50	$235.50
Purchase #6	$48.26	13.173%	$54.6173	$54.62	$54.60	$54.60
Purchase #7	$54.52	9.862%	$59.8968	$59.90	$59.90	$59.90
7 purchase totals =	$673.64		$735.5848	$735.60	$735.60	$735.50