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	$212.86	4.491%	$222.4195	$222.42	$222.40	$222.40
Purchase #2	$37.55	10.579%	$41.5224	$41.52	$41.50	$41.50
Purchase #3	$65.93	8.481%	$71.5215	$71.52	$71.50	$71.50
Purchase #4	$230.60	7.839%	$248.6767	$248.68	$248.70	$248.70
Purchase #5	$155.44	10.862%	$172.3239	$172.32	$172.30	$172.30
Purchase #6	$15.28	6.377%	$16.2544	$16.25	$16.25	$16.30
Purchase #7	$130.65	10.152%	$143.9136	$143.91	$143.90	$143.90
7 purchase totals =	$848.31		$916.6320	$916.62	$916.55	$916.60