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	$100.70	11.125%	$111.9029	$111.90	$111.90	$111.90
Purchase #2	$143.41	3.527%	$148.4681	$148.47	$148.45	$148.50
Purchase #3	$233.46	9.793%	$256.3227	$256.32	$256.30	$256.30
Purchase #4	$41.58	3.554%	$43.0578	$43.06	$43.05	$43.10
Purchase #5	$245.87	12.188%	$275.8366	$275.84	$275.85	$275.80
Purchase #6	$123.72	11.147%	$137.5111	$137.51	$137.50	$137.50
Purchase #7	$240.81	5.811%	$254.8035	$254.80	$254.80	$254.80
7 purchase totals =	$1,129.55		$1,227.9027	$1,227.90	$1,227.85	$1,227.90