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	$156.77	13.416%	$177.8023	$177.80	$177.80	$177.80
Purchase #2	$19.31	8.162%	$20.8861	$20.89	$20.90	$20.90
Purchase #3	$159.73	8.310%	$173.0036	$173.00	$173.00	$173.00
Purchase #4	$249.71	11.445%	$278.2893	$278.29	$278.30	$278.30
Purchase #5	$200.60	10.434%	$221.5306	$221.53	$221.55	$221.50
Purchase #6	$161.82	10.301%	$178.4891	$178.49	$178.50	$178.50
Purchase #7	$220.52	13.636%	$250.5901	$250.59	$250.60	$250.60
7 purchase totals =	$1,168.46		$1,300.5911	$1,300.59	$1,300.65	$1,300.60