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	$146.29	10.156%	$161.1472	$161.15	$161.15	$161.10
Purchase #2	$228.74	11.753%	$255.6238	$255.62	$255.60	$255.60
Purchase #3	$188.48	13.858%	$214.5996	$214.60	$214.60	$214.60
Purchase #4	$123.90	5.469%	$130.6761	$130.68	$130.70	$130.70
Purchase #5	$137.43	8.362%	$148.9219	$148.92	$148.90	$148.90
Purchase #6	$40.44	5.253%	$42.5643	$42.56	$42.55	$42.60
Purchase #7	$44.88	6.559%	$47.8237	$47.82	$47.80	$47.80
7 purchase totals =	$910.16		$1,001.3566	$1,001.35	$1,001.30	$1,001.30