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	$151.72	13.480%	$172.1719	$172.17	$172.15	$172.20
Purchase #2	$56.28	7.483%	$60.4914	$60.49	$60.50	$60.50
Purchase #3	$227.60	3.612%	$235.8209	$235.82	$235.80	$235.80
Purchase #4	$71.91	13.802%	$81.835	$81.84	$81.85	$81.80
Purchase #5	$36.38	11.328%	$40.5011	$40.50	$40.50	$40.50
Purchase #6	$62.68	4.477%	$65.4862	$65.49	$65.50	$65.50
Purchase #7	$22.45	6.834%	$23.9842	$23.98	$24.00	$24.00
7 purchase totals =	$629.02		$680.2907	$680.29	$680.30	$680.30