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	$17.75	5.718%	$18.7649	$18.76	$18.75	$18.80
Purchase #2	$244.28	8.140%	$264.1644	$264.16	$264.15	$264.20
Purchase #3	$60.34	12.516%	$67.8922	$67.89	$67.90	$67.90
Purchase #4	$203.49	5.353%	$214.3828	$214.38	$214.40	$214.40
Purchase #5	$34.85	10.164%	$38.3922	$38.39	$38.40	$38.40
Purchase #6	$130.29	9.819%	$143.0832	$143.08	$143.10	$143.10
Purchase #7	$11.55	11.693%	$12.9005	$12.90	$12.90	$12.90
7 purchase totals =	$702.55		$759.5802	$759.56	$759.60	$759.70