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	$19.82	9.585%	$21.7197	$21.72	$21.70	$21.70
Purchase #2	$53.86	11.649%	$60.1342	$60.13	$60.15	$60.10
Purchase #3	$233.61	13.817%	$265.8879	$265.89	$265.90	$265.90
Purchase #4	$119.34	3.422%	$123.4238	$123.42	$123.40	$123.40
Purchase #5	$195.93	13.123%	$221.6419	$221.64	$221.65	$221.60
Purchase #6	$50.60	13.718%	$57.5413	$57.54	$57.55	$57.50
Purchase #7	$170.99	11.331%	$190.3649	$190.36	$190.35	$190.40
7 purchase totals =	$844.15		$940.7137	$940.70	$940.70	$940.60