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	$14.49	7.406%	$15.5631	$15.56	$15.55	$15.60
Purchase #2	$108.43	3.237%	$111.9399	$111.94	$111.95	$111.90
Purchase #3	$54.66	4.572%	$57.1591	$57.16	$57.15	$57.20
Purchase #4	$231.59	7.137%	$248.1186	$248.12	$248.10	$248.10
Purchase #5	$175.29	8.550%	$190.2773	$190.28	$190.30	$190.30
Purchase #6	$226.85	10.144%	$249.8617	$249.86	$249.85	$249.90
Purchase #7	$78.43	5.696%	$82.8974	$82.90	$82.90	$82.90
7 purchase totals =	$889.74		$955.8171	$955.82	$955.80	$955.90