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	$46.73	4.644%	$48.9001	$48.90	$48.90	$48.90
Purchase #2	$142.69	13.640%	$162.1529	$162.15	$162.15	$162.20
Purchase #3	$44.50	4.609%	$46.551	$46.55	$46.55	$46.60
Purchase #4	$111.92	11.216%	$124.4729	$124.47	$124.45	$124.50
Purchase #5	$105.35	6.867%	$112.5844	$112.58	$112.60	$112.60
Purchase #6	$109.27	12.845%	$123.3057	$123.31	$123.30	$123.30
Purchase #7	$16.70	7.468%	$17.9472	$17.95	$17.95	$17.90
7 purchase totals =	$577.16		$635.9142	$635.91	$635.90	$636.00