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	$48.70	7.382%	$52.295	$52.30	$52.30	$52.30
Purchase #2	$128.38	6.724%	$137.0123	$137.01	$137.00	$137.00
Purchase #3	$122.88	12.536%	$138.2842	$138.28	$138.30	$138.30
Purchase #4	$49.56	11.318%	$55.1692	$55.17	$55.15	$55.20
Purchase #5	$155.71	10.119%	$171.4663	$171.47	$171.45	$171.50
Purchase #6	$96.27	3.327%	$99.4729	$99.47	$99.45	$99.50
Purchase #7	$31.83	8.648%	$34.5827	$34.58	$34.60	$34.60
7 purchase totals =	$633.33		$688.2826	$688.28	$688.25	$688.40