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	$159.56	12.494%	$179.4954	$179.50	$179.50	$179.50
Purchase #2	$80.25	4.852%	$84.1437	$84.14	$84.15	$84.10
Purchase #3	$229.79	11.733%	$256.7513	$256.75	$256.75	$256.80
Purchase #4	$157.92	8.483%	$171.3164	$171.32	$171.30	$171.30
Purchase #5	$96.91	8.612%	$105.2559	$105.26	$105.25	$105.30
Purchase #6	$103.42	12.709%	$116.5636	$116.56	$116.55	$116.60
Purchase #7	$217.37	11.167%	$241.6437	$241.64	$241.65	$241.60
7 purchase totals =	$1,045.22		$1,155.1700	$1,155.17	$1,155.15	$1,155.20