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	$66.72	8.316%	$72.2684	$72.27	$72.25	$72.30
Purchase #2	$103.77	13.591%	$117.8734	$117.87	$117.85	$117.90
Purchase #3	$87.96	9.328%	$96.1649	$96.16	$96.15	$96.20
Purchase #4	$241.96	13.169%	$273.8237	$273.82	$273.80	$273.80
Purchase #5	$86.62	3.563%	$89.7063	$89.71	$89.70	$89.70
Purchase #6	$217.42	13.804%	$247.4327	$247.43	$247.45	$247.40
Purchase #7	$127.45	8.240%	$137.9519	$137.95	$137.95	$138.00
7 purchase totals =	$931.90		$1,035.2213	$1,035.21	$1,035.15	$1,035.30