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	$159.57	8.792%	$173.5994	$173.60	$173.60	$173.60
Purchase #2	$176.51	5.211%	$185.7079	$185.71	$185.70	$185.70
Purchase #3	$108.79	9.784%	$119.434	$119.43	$119.45	$119.40
Purchase #4	$88.52	11.857%	$99.0158	$99.02	$99.00	$99.00
Purchase #5	$127.72	6.484%	$136.0014	$136.00	$136.00	$136.00
Purchase #6	$118.54	7.605%	$127.555	$127.56	$127.55	$127.60
Purchase #7	$119.32	10.707%	$132.0956	$132.10	$132.10	$132.10
7 purchase totals =	$898.97		$973.4091	$973.42	$973.40	$973.40