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	$22.70	12.335%	$25.5	$25.50	$25.50	$25.50
Purchase #2	$50.83	10.361%	$56.0965	$56.10	$56.10	$56.10
Purchase #3	$209.60	6.313%	$222.832	$222.83	$222.85	$222.80
Purchase #4	$152.65	12.486%	$171.7099	$171.71	$171.70	$171.70
Purchase #5	$213.83	7.749%	$230.3997	$230.40	$230.40	$230.40
Purchase #6	$219.81	13.773%	$250.0844	$250.08	$250.10	$250.10
Purchase #7	$112.54	4.106%	$117.1609	$117.16	$117.15	$117.20
7 purchase totals =	$981.96		$1,073.7834	$1,073.78	$1,073.80	$1,073.80