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	$128.84	8.105%	$139.2825	$139.28	$139.30	$139.30
Purchase #2	$230.77	9.592%	$252.9055	$252.91	$252.90	$252.90
Purchase #3	$88.75	11.558%	$99.0077	$99.01	$99.00	$99.00
Purchase #4	$40.60	12.797%	$45.7956	$45.80	$45.80	$45.80
Purchase #5	$225.33	3.254%	$232.6622	$232.66	$232.65	$232.70
Purchase #6	$100.78	10.164%	$111.0233	$111.02	$111.00	$111.00
Purchase #7	$31.33	13.575%	$35.583	$35.58	$35.60	$35.60
7 purchase totals =	$846.40		$916.2598	$916.26	$916.25	$916.30