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	$244.38	11.677%	$272.9163	$272.92	$272.90	$272.90
Purchase #2	$240.28	13.223%	$272.0522	$272.05	$272.05	$272.10
Purchase #3	$155.38	9.678%	$170.4177	$170.42	$170.40	$170.40
Purchase #4	$145.52	5.181%	$153.0594	$153.06	$153.05	$153.10
Purchase #5	$130.37	6.822%	$139.2638	$139.26	$139.25	$139.30
Purchase #6	$96.61	4.396%	$100.857	$100.86	$100.85	$100.90
Purchase #7	$74.47	8.838%	$81.0517	$81.05	$81.05	$81.10
7 purchase totals =	$1,087.01		$1,189.6181	$1,189.62	$1,189.55	$1,189.80