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	$50.46	6.368%	$53.6733	$53.67	$53.65	$53.70
Purchase #2	$157.54	13.137%	$178.236	$178.24	$178.25	$178.20
Purchase #3	$90.51	6.606%	$96.4891	$96.49	$96.50	$96.50
Purchase #4	$238.70	11.782%	$266.8236	$266.82	$266.80	$266.80
Purchase #5	$70.87	12.117%	$79.4573	$79.46	$79.45	$79.50
Purchase #6	$98.31	13.381%	$111.4649	$111.46	$111.45	$111.50
Purchase #7	$87.51	13.170%	$99.0351	$99.04	$99.05	$99.00
7 purchase totals =	$793.90		$885.1793	$885.18	$885.15	$885.20