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	$78.35	5.168%	$82.3991	$82.40	$82.40	$82.40
Purchase #2	$59.93	4.818%	$62.8174	$62.82	$62.80	$62.80
Purchase #3	$5.84	6.145%	$6.1989	$6.20	$6.20	$6.20
Purchase #4	$74.91	10.726%	$82.9448	$82.94	$82.95	$82.90
Purchase #5	$136.41	4.143%	$142.0615	$142.06	$142.05	$142.10
Purchase #6	$212.72	6.168%	$225.8406	$225.84	$225.85	$225.80
Purchase #7	$106.56	10.228%	$117.459	$117.46	$117.45	$117.50
7 purchase totals =	$674.72		$719.7213	$719.72	$719.70	$719.70