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	$26.92	10.449%	$29.7329	$29.73	$29.75	$29.70
Purchase #2	$181.70	10.144%	$200.1316	$200.13	$200.15	$200.10
Purchase #3	$70.56	3.195%	$72.8144	$72.81	$72.80	$72.80
Purchase #4	$141.42	8.407%	$153.3092	$153.31	$153.30	$153.30
Purchase #5	$74.81	12.247%	$83.972	$83.97	$83.95	$84.00
Purchase #6	$111.86	13.824%	$127.3235	$127.32	$127.30	$127.30
Purchase #7	$190.65	5.301%	$200.7564	$200.76	$200.75	$200.80
7 purchase totals =	$797.92		$868.0400	$868.03	$868.00	$868.00