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	$209.52	5.715%	$221.4941	$221.49	$221.50	$221.50
Purchase #2	$155.71	10.519%	$172.0891	$172.09	$172.10	$172.10
Purchase #3	$39.29	5.592%	$41.4871	$41.49	$41.50	$41.50
Purchase #4	$125.78	5.546%	$132.7558	$132.76	$132.75	$132.80
Purchase #5	$54.75	3.836%	$56.8502	$56.85	$56.85	$56.90
Purchase #6	$158.46	7.577%	$170.4665	$170.47	$170.45	$170.50
Purchase #7	$82.31	6.821%	$87.9244	$87.92	$87.90	$87.90
7 purchase totals =	$825.82		$883.0672	$883.07	$883.05	$883.20