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	$230.52	9.812%	$253.1386	$253.14	$253.15	$253.10
Purchase #2	$165.47	3.436%	$171.1555	$171.16	$171.15	$171.20
Purchase #3	$43.92	3.749%	$45.5666	$45.57	$45.55	$45.60
Purchase #4	$222.76	7.143%	$238.6717	$238.67	$238.65	$238.70
Purchase #5	$147.29	4.437%	$153.8253	$153.83	$153.85	$153.80
Purchase #6	$40.32	6.729%	$43.0331	$43.03	$43.05	$43.00
Purchase #7	$99.25	12.262%	$111.42	$111.42	$111.40	$111.40
7 purchase totals =	$949.53		$1,016.8108	$1,016.82	$1,016.80	$1,016.80