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	$170.31	8.615%	$184.9822	$184.98	$185.00	$185.00
Purchase #2	$111.47	10.658%	$123.3505	$123.35	$123.35	$123.40
Purchase #3	$182.53	8.131%	$197.3715	$197.37	$197.35	$197.40
Purchase #4	$207.89	12.195%	$233.2422	$233.24	$233.25	$233.20
Purchase #5	$18.52	13.307%	$20.9845	$20.98	$21.00	$21.00
Purchase #6	$60.40	7.769%	$65.0925	$65.09	$65.10	$65.10
Purchase #7	$126.64	11.442%	$141.1301	$141.13	$141.15	$141.10
7 purchase totals =	$877.76		$966.1535	$966.14	$966.20	$966.20