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	$181.70	5.106%	$190.9776	$190.98	$191.00	$191.00
Purchase #2	$103.43	7.603%	$111.2938	$111.29	$111.30	$111.30
Purchase #3	$129.32	11.380%	$144.0366	$144.04	$144.05	$144.00
Purchase #4	$129.90	8.684%	$141.1805	$141.18	$141.20	$141.20
Purchase #5	$97.86	7.774%	$105.4676	$105.47	$105.45	$105.50
Purchase #6	$57.54	8.353%	$62.3463	$62.35	$62.35	$62.30
Purchase #7	$68.78	13.182%	$77.8466	$77.85	$77.85	$77.80
7 purchase totals =	$768.53		$833.1490	$833.16	$833.20	$833.10