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	$80.54	3.491%	$83.3517	$83.35	$83.35	$83.40
Purchase #2	$95.45	4.823%	$100.0536	$100.05	$100.05	$100.10
Purchase #3	$149.75	6.329%	$159.2277	$159.23	$159.25	$159.20
Purchase #4	$140.86	4.664%	$147.4297	$147.43	$147.45	$147.40
Purchase #5	$46.85	4.710%	$49.0566	$49.06	$49.05	$49.10
Purchase #6	$103.83	13.125%	$117.4577	$117.46	$117.45	$117.50
Purchase #7	$248.82	10.381%	$274.65	$274.65	$274.65	$274.70
7 purchase totals =	$866.10		$931.2270	$931.23	$931.25	$931.40