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	$79.32	13.360%	$89.9172	$89.92	$89.90	$89.90
Purchase #2	$66.52	11.840%	$74.396	$74.40	$74.40	$74.40
Purchase #3	$18.59	12.185%	$20.8552	$20.86	$20.85	$20.90
Purchase #4	$217.31	7.643%	$233.919	$233.92	$233.90	$233.90
Purchase #5	$22.69	11.264%	$25.2458	$25.25	$25.25	$25.20
Purchase #6	$166.94	13.535%	$189.5353	$189.54	$189.55	$189.50
Purchase #7	$9.56	7.784%	$10.3042	$10.30	$10.30	$10.30
7 purchase totals =	$580.93		$644.1727	$644.19	$644.15	$644.10