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	$20.86	4.770%	$21.855	$21.86	$21.85	$21.90
Purchase #2	$118.61	7.512%	$127.52	$127.52	$127.50	$127.50
Purchase #3	$192.82	4.166%	$200.8529	$200.85	$200.85	$200.90
Purchase #4	$18.87	11.209%	$20.9851	$20.99	$21.00	$21.00
Purchase #5	$246.60	8.782%	$268.2564	$268.26	$268.25	$268.30
Purchase #6	$241.72	6.592%	$257.6542	$257.65	$257.65	$257.70
Purchase #7	$155.40	10.298%	$171.4031	$171.40	$171.40	$171.40
7 purchase totals =	$994.88		$1,068.5267	$1,068.53	$1,068.50	$1,068.70