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	$222.71	10.533%	$246.168	$246.17	$246.15	$246.20
Purchase #2	$135.42	8.162%	$146.473	$146.47	$146.45	$146.50
Purchase #3	$47.82	13.192%	$54.1284	$54.13	$54.15	$54.10
Purchase #4	$75.55	3.503%	$78.1965	$78.20	$78.20	$78.20
Purchase #5	$204.35	13.466%	$231.8678	$231.87	$231.85	$231.90
Purchase #6	$115.25	11.821%	$128.8737	$128.87	$128.85	$128.90
Purchase #7	$40.80	6.169%	$43.317	$43.32	$43.30	$43.30
7 purchase totals =	$841.90		$929.0244	$929.03	$928.95	$929.10