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	$242.86	5.466%	$256.1347	$256.13	$256.15	$256.10
Purchase #2	$181.29	12.641%	$204.2069	$204.21	$204.20	$204.20
Purchase #3	$240.37	7.407%	$258.1742	$258.17	$258.15	$258.20
Purchase #4	$90.72	10.289%	$100.0542	$100.05	$100.05	$100.10
Purchase #5	$212.36	4.105%	$221.0774	$221.08	$221.10	$221.10
Purchase #6	$68.86	5.663%	$72.7595	$72.76	$72.75	$72.80
Purchase #7	$192.82	11.390%	$214.7822	$214.78	$214.80	$214.80
7 purchase totals =	$1,229.28		$1,327.1891	$1,327.18	$1,327.20	$1,327.30