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	$5.86	5.204%	$6.165	$6.17	$6.15	$6.20
Purchase #2	$88.28	11.620%	$98.5381	$98.54	$98.55	$98.50
Purchase #3	$80.55	12.284%	$90.4448	$90.44	$90.45	$90.40
Purchase #4	$30.77	4.365%	$32.1131	$32.11	$32.10	$32.10
Purchase #5	$141.74	11.856%	$158.5447	$158.54	$158.55	$158.50
Purchase #6	$236.29	9.208%	$258.0476	$258.05	$258.05	$258.00
Purchase #7	$9.41	13.293%	$10.6609	$10.66	$10.65	$10.70
7 purchase totals =	$592.90		$654.5142	$654.51	$654.50	$654.40