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	$106.72	4.769%	$111.8095	$111.81	$111.80	$111.80
Purchase #2	$86.72	6.852%	$92.6621	$92.66	$92.65	$92.70
Purchase #3	$85.93	7.618%	$92.4761	$92.48	$92.50	$92.50
Purchase #4	$98.60	8.475%	$106.9564	$106.96	$106.95	$107.00
Purchase #5	$60.42	3.682%	$62.6447	$62.64	$62.65	$62.60
Purchase #6	$87.66	3.573%	$90.7921	$90.79	$90.80	$90.80
Purchase #7	$134.59	3.123%	$138.7932	$138.79	$138.80	$138.80
7 purchase totals =	$660.64		$696.1341	$696.13	$696.15	$696.20