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	$173.73	8.737%	$188.9088	$188.91	$188.90	$188.90
Purchase #2	$244.29	5.558%	$257.8676	$257.87	$257.85	$257.90
Purchase #3	$170.84	6.222%	$181.4697	$181.47	$181.45	$181.50
Purchase #4	$20.56	5.863%	$21.7654	$21.77	$21.75	$21.80
Purchase #5	$118.37	10.845%	$131.2072	$131.21	$131.20	$131.20
Purchase #6	$60.91	7.282%	$65.3455	$65.35	$65.35	$65.30
Purchase #7	$78.30	5.831%	$82.8657	$82.87	$82.85	$82.90
7 purchase totals =	$867.00		$929.4299	$929.45	$929.35	$929.50