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	$114.78	11.822%	$128.3493	$128.35	$128.35	$128.30
Purchase #2	$202.88	9.328%	$221.8046	$221.80	$221.80	$221.80
Purchase #3	$14.45	7.109%	$15.4773	$15.48	$15.50	$15.50
Purchase #4	$48.26	12.215%	$54.155	$54.16	$54.15	$54.20
Purchase #5	$158.57	8.146%	$171.4871	$171.49	$171.50	$171.50
Purchase #6	$63.65	13.431%	$72.1988	$72.20	$72.20	$72.20
Purchase #7	$43.81	12.836%	$49.4335	$49.43	$49.45	$49.40
7 purchase totals =	$646.40		$712.9056	$712.91	$712.95	$712.90