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	$109.37	8.209%	$118.3482	$118.35	$118.35	$118.30
Purchase #2	$11.52	5.134%	$12.1114	$12.11	$12.10	$12.10
Purchase #3	$124.35	3.319%	$128.4772	$128.48	$128.50	$128.50
Purchase #4	$86.89	3.753%	$90.151	$90.15	$90.15	$90.20
Purchase #5	$42.89	10.621%	$47.4453	$47.45	$47.45	$47.40
Purchase #6	$148.65	5.550%	$156.9001	$156.90	$156.90	$156.90
Purchase #7	$78.90	9.694%	$86.5486	$86.55	$86.55	$86.50
7 purchase totals =	$602.57		$639.9818	$639.99	$640.00	$639.90