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	$63.60	3.697%	$65.9513	$65.95	$65.95	$66.00
Purchase #2	$136.55	7.455%	$146.7298	$146.73	$146.75	$146.70
Purchase #3	$98.76	12.560%	$111.1643	$111.16	$111.15	$111.20
Purchase #4	$53.85	10.584%	$59.5495	$59.55	$59.55	$59.50
Purchase #5	$106.45	6.593%	$113.4682	$113.47	$113.45	$113.50
Purchase #6	$246.68	8.520%	$267.6971	$267.70	$267.70	$267.70
Purchase #7	$35.54	7.739%	$38.2904	$38.29	$38.30	$38.30
7 purchase totals =	$741.43		$802.8506	$802.85	$802.85	$802.90