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	$248.33	8.349%	$269.0631	$269.06	$269.05	$269.10
Purchase #2	$66.34	9.164%	$72.4194	$72.42	$72.40	$72.40
Purchase #3	$137.91	7.380%	$148.0878	$148.09	$148.10	$148.10
Purchase #4	$152.52	4.111%	$158.7901	$158.79	$158.80	$158.80
Purchase #5	$114.29	4.419%	$119.3405	$119.34	$119.35	$119.30
Purchase #6	$34.25	11.758%	$38.2771	$38.28	$38.30	$38.30
Purchase #7	$60.43	8.743%	$65.7134	$65.71	$65.70	$65.70
7 purchase totals =	$814.07		$871.6914	$871.69	$871.70	$871.70