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	$14.32	9.371%	$15.6619	$15.66	$15.65	$15.70
Purchase #2	$47.73	9.667%	$52.3441	$52.34	$52.35	$52.30
Purchase #3	$20.40	10.752%	$22.5934	$22.59	$22.60	$22.60
Purchase #4	$233.86	7.869%	$252.2624	$252.26	$252.25	$252.30
Purchase #5	$80.62	10.633%	$89.1923	$89.19	$89.20	$89.20
Purchase #6	$43.52	5.304%	$45.8283	$45.83	$45.85	$45.80
Purchase #7	$151.62	4.478%	$158.4095	$158.41	$158.40	$158.40
7 purchase totals =	$592.07		$636.2919	$636.28	$636.30	$636.30