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	$12.61	4.249%	$13.1458	$13.15	$13.15	$13.10
Purchase #2	$95.81	6.317%	$101.8623	$101.86	$101.85	$101.90
Purchase #3	$121.78	4.738%	$127.5499	$127.55	$127.55	$127.50
Purchase #4	$54.39	3.125%	$56.0897	$56.09	$56.10	$56.10
Purchase #5	$191.98	12.133%	$215.2729	$215.27	$215.25	$215.30
Purchase #6	$60.43	9.684%	$66.282	$66.28	$66.30	$66.30
Purchase #7	$100.70	9.274%	$110.0389	$110.04	$110.05	$110.00
7 purchase totals =	$637.70		$690.2415	$690.24	$690.25	$690.20