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	$32.95	5.525%	$34.7705	$34.77	$34.75	$34.80
Purchase #2	$106.60	4.512%	$111.4098	$111.41	$111.40	$111.40
Purchase #3	$158.56	11.265%	$176.4218	$176.42	$176.40	$176.40
Purchase #4	$49.77	7.391%	$53.4485	$53.45	$53.45	$53.40
Purchase #5	$209.34	10.682%	$231.7017	$231.70	$231.70	$231.70
Purchase #6	$105.28	5.636%	$111.2136	$111.21	$111.20	$111.20
Purchase #7	$107.75	5.698%	$113.8896	$113.89	$113.90	$113.90
7 purchase totals =	$770.25		$832.8555	$832.85	$832.80	$832.80