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	$74.67	7.400%	$80.1956	$80.20	$80.20	$80.20
Purchase #2	$83.92	7.707%	$90.3877	$90.39	$90.40	$90.40
Purchase #3	$211.49	12.130%	$237.1437	$237.14	$237.15	$237.10
Purchase #4	$81.87	13.126%	$92.6163	$92.62	$92.60	$92.60
Purchase #5	$42.61	7.615%	$45.8548	$45.85	$45.85	$45.90
Purchase #6	$106.78	4.731%	$111.8318	$111.83	$111.85	$111.80
Purchase #7	$218.60	6.861%	$233.5981	$233.60	$233.60	$233.60
7 purchase totals =	$819.94		$891.6280	$891.63	$891.65	$891.60