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	$16.59	13.711%	$18.8647	$18.86	$18.85	$18.90
Purchase #2	$149.61	3.548%	$154.9182	$154.92	$154.90	$154.90
Purchase #3	$152.62	4.279%	$159.1506	$159.15	$159.15	$159.20
Purchase #4	$148.83	11.753%	$166.322	$166.32	$166.30	$166.30
Purchase #5	$241.68	8.767%	$262.8681	$262.87	$262.85	$262.90
Purchase #6	$151.92	13.717%	$172.7589	$172.76	$172.75	$172.80
Purchase #7	$76.70	6.483%	$81.6725	$81.67	$81.65	$81.70
7 purchase totals =	$937.95		$1,016.5550	$1,016.55	$1,016.45	$1,016.70