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	$98.98	4.207%	$103.1441	$103.14	$103.15	$103.10
Purchase #2	$244.77	3.152%	$252.4852	$252.49	$252.50	$252.50
Purchase #3	$26.44	3.142%	$27.2707	$27.27	$27.25	$27.30
Purchase #4	$57.39	11.258%	$63.851	$63.85	$63.85	$63.90
Purchase #5	$78.90	5.294%	$83.077	$83.08	$83.10	$83.10
Purchase #6	$61.27	7.842%	$66.0748	$66.07	$66.05	$66.10
Purchase #7	$35.87	13.198%	$40.6041	$40.60	$40.60	$40.60
7 purchase totals =	$603.62		$636.5069	$636.50	$636.50	$636.60