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	$45.86	12.229%	$51.4682	$51.47	$51.45	$51.50
Purchase #2	$166.42	3.733%	$172.6325	$172.63	$172.65	$172.60
Purchase #3	$48.47	3.437%	$50.1359	$50.14	$50.15	$50.10
Purchase #4	$40.66	6.466%	$43.2891	$43.29	$43.30	$43.30
Purchase #5	$44.39	13.576%	$50.4164	$50.42	$50.40	$50.40
Purchase #6	$102.90	8.801%	$111.9562	$111.96	$111.95	$112.00
Purchase #7	$166.97	8.350%	$180.912	$180.91	$180.90	$180.90
7 purchase totals =	$615.67		$660.8103	$660.82	$660.80	$660.80