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	$103.70	11.746%	$115.8806	$115.88	$115.90	$115.90
Purchase #2	$131.91	11.304%	$146.8211	$146.82	$146.80	$146.80
Purchase #3	$139.73	8.509%	$151.6196	$151.62	$151.60	$151.60
Purchase #4	$77.95	11.490%	$86.9065	$86.91	$86.90	$86.90
Purchase #5	$28.82	9.499%	$31.5576	$31.56	$31.55	$31.60
Purchase #6	$11.28	5.398%	$11.8889	$11.89	$11.90	$11.90
Purchase #7	$142.77	7.255%	$153.128	$153.13	$153.15	$153.10
7 purchase totals =	$636.16		$697.8023	$697.81	$697.80	$697.80