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	$15.89	7.617%	$17.1003	$17.10	$17.10	$17.10
Purchase #2	$89.75	7.111%	$96.1321	$96.13	$96.15	$96.10
Purchase #3	$17.61	11.476%	$19.6309	$19.63	$19.65	$19.60
Purchase #4	$175.73	10.726%	$194.5788	$194.58	$194.60	$194.60
Purchase #5	$235.82	13.663%	$268.0401	$268.04	$268.05	$268.00
Purchase #6	$208.47	8.157%	$225.4749	$225.47	$225.45	$225.50
Purchase #7	$85.61	4.667%	$89.6054	$89.61	$89.60	$89.60
7 purchase totals =	$828.88		$910.5625	$910.56	$910.60	$910.50