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	$92.76	8.541%	$100.6826	$100.68	$100.70	$100.70
Purchase #2	$205.37	13.761%	$233.631	$233.63	$233.65	$233.60
Purchase #3	$96.52	3.862%	$100.2476	$100.25	$100.25	$100.20
Purchase #4	$208.89	6.842%	$223.1823	$223.18	$223.20	$223.20
Purchase #5	$216.86	6.449%	$230.8453	$230.85	$230.85	$230.80
Purchase #6	$101.80	5.847%	$107.7522	$107.75	$107.75	$107.80
Purchase #7	$127.36	10.143%	$140.2781	$140.28	$140.30	$140.30
7 purchase totals =	$1,049.56		$1,136.6191	$1,136.62	$1,136.70	$1,136.60