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	$12.92	6.802%	$13.7988	$13.80	$13.80	$13.80
Purchase #2	$5.83	5.823%	$6.1695	$6.17	$6.15	$6.20
Purchase #3	$238.32	13.131%	$269.6138	$269.61	$269.60	$269.60
Purchase #4	$68.74	11.732%	$76.8046	$76.80	$76.80	$76.80
Purchase #5	$10.31	6.820%	$11.0131	$11.01	$11.00	$11.00
Purchase #6	$35.52	7.726%	$38.2643	$38.26	$38.25	$38.30
Purchase #7	$98.76	12.561%	$111.1652	$111.17	$111.15	$111.20
7 purchase totals =	$470.40		$526.8293	$526.82	$526.75	$526.90