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	$19.72	13.722%	$22.426	$22.43	$22.45	$22.40
Purchase #2	$17.60	6.705%	$18.7801	$18.78	$18.80	$18.80
Purchase #3	$181.92	8.152%	$196.7501	$196.75	$196.75	$196.80
Purchase #4	$211.33	13.325%	$239.4897	$239.49	$239.50	$239.50
Purchase #5	$38.79	8.848%	$42.2221	$42.22	$42.20	$42.20
Purchase #6	$68.36	13.338%	$77.4779	$77.48	$77.50	$77.50
Purchase #7	$31.71	10.825%	$35.1426	$35.14	$35.15	$35.10
7 purchase totals =	$569.43		$632.2885	$632.29	$632.35	$632.30