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	$70.51	11.358%	$78.5185	$78.52	$78.50	$78.50
Purchase #2	$20.27	10.726%	$22.4442	$22.44	$22.45	$22.40
Purchase #3	$106.76	11.102%	$118.6125	$118.61	$118.60	$118.60
Purchase #4	$165.32	4.197%	$172.2585	$172.26	$172.25	$172.30
Purchase #5	$84.88	13.239%	$96.1173	$96.12	$96.10	$96.10
Purchase #6	$238.57	11.593%	$266.2274	$266.23	$266.25	$266.20
Purchase #7	$162.98	13.386%	$184.7965	$184.80	$184.80	$184.80
7 purchase totals =	$849.29		$938.9749	$938.98	$938.95	$938.90