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	$70.80	11.783%	$79.1424	$79.14	$79.15	$79.10
Purchase #2	$248.56	8.714%	$270.2195	$270.22	$270.20	$270.20
Purchase #3	$214.42	6.787%	$228.9727	$228.97	$228.95	$229.00
Purchase #4	$243.50	11.503%	$271.5098	$271.51	$271.50	$271.50
Purchase #5	$9.89	11.250%	$11.0026	$11.00	$11.00	$11.00
Purchase #6	$91.28	10.232%	$100.6198	$100.62	$100.60	$100.60
Purchase #7	$134.57	3.634%	$139.4603	$139.46	$139.45	$139.50
7 purchase totals =	$1,013.02		$1,100.9271	$1,100.92	$1,100.85	$1,100.90