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	$101.83	8.821%	$110.8124	$110.81	$110.80	$110.80
Purchase #2	$44.94	3.772%	$46.6351	$46.64	$46.65	$46.60
Purchase #3	$218.54	10.471%	$241.4233	$241.42	$241.40	$241.40
Purchase #4	$81.74	10.476%	$90.3031	$90.30	$90.30	$90.30
Purchase #5	$19.37	8.446%	$21.006	$21.01	$21.00	$21.00
Purchase #6	$9.31	12.716%	$10.4939	$10.49	$10.50	$10.50
Purchase #7	$42.89	5.289%	$45.1585	$45.16	$45.15	$45.20
7 purchase totals =	$518.62		$565.8323	$565.83	$565.80	$565.80