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	$121.64	13.122%	$137.6016	$137.60	$137.60	$137.60
Purchase #2	$58.54	11.763%	$65.4261	$65.43	$65.45	$65.40
Purchase #3	$99.98	4.296%	$104.2751	$104.28	$104.30	$104.30
Purchase #4	$242.56	5.177%	$255.1173	$255.12	$255.10	$255.10
Purchase #5	$107.37	13.870%	$122.2622	$122.26	$122.25	$122.30
Purchase #6	$46.90	13.364%	$53.1677	$53.17	$53.15	$53.20
Purchase #7	$219.59	6.126%	$233.0421	$233.04	$233.05	$233.00
7 purchase totals =	$896.58		$970.8921	$970.90	$970.90	$970.90