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	$74.39	4.659%	$77.8558	$77.86	$77.85	$77.90
Purchase #2	$60.49	10.104%	$66.6019	$66.60	$66.60	$66.60
Purchase #3	$84.50	8.113%	$91.3555	$91.36	$91.35	$91.40
Purchase #4	$87.56	9.464%	$95.8467	$95.85	$95.85	$95.80
Purchase #5	$197.88	12.302%	$222.2232	$222.22	$222.20	$222.20
Purchase #6	$131.37	13.502%	$149.1076	$149.11	$149.10	$149.10
Purchase #7	$151.26	10.336%	$166.8942	$166.89	$166.90	$166.90
7 purchase totals =	$787.45		$869.8849	$869.89	$869.85	$869.90