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	$167.46	5.188%	$176.1478	$176.15	$176.15	$176.10
Purchase #2	$145.83	5.550%	$153.9236	$153.92	$153.90	$153.90
Purchase #3	$243.86	6.230%	$259.0525	$259.05	$259.05	$259.10
Purchase #4	$84.64	11.530%	$94.399	$94.40	$94.40	$94.40
Purchase #5	$21.72	9.641%	$23.814	$23.81	$23.80	$23.80
Purchase #6	$103.30	8.239%	$111.8109	$111.81	$111.80	$111.80
Purchase #7	$156.41	10.296%	$172.514	$172.51	$172.50	$172.50
7 purchase totals =	$923.22		$991.6618	$991.65	$991.60	$991.60