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	$43.33	8.861%	$47.1695	$47.17	$47.15	$47.20
Purchase #2	$161.51	10.656%	$178.7205	$178.72	$178.70	$178.70
Purchase #3	$124.33	13.603%	$141.2426	$141.24	$141.25	$141.20
Purchase #4	$131.39	10.806%	$145.588	$145.59	$145.60	$145.60
Purchase #5	$234.48	8.147%	$253.5831	$253.58	$253.60	$253.60
Purchase #6	$73.80	9.503%	$80.8132	$80.81	$80.80	$80.80
Purchase #7	$165.52	4.798%	$173.4616	$173.46	$173.45	$173.50
7 purchase totals =	$934.36		$1,020.5785	$1,020.57	$1,020.55	$1,020.60