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	$235.41	11.680%	$262.9059	$262.91	$262.90	$262.90
Purchase #2	$55.32	13.242%	$62.6455	$62.65	$62.65	$62.60
Purchase #3	$99.56	10.294%	$109.8087	$109.81	$109.80	$109.80
Purchase #4	$128.80	5.119%	$135.3933	$135.39	$135.40	$135.40
Purchase #5	$51.93	8.827%	$56.5139	$56.51	$56.50	$56.50
Purchase #6	$11.49	5.701%	$12.145	$12.15	$12.15	$12.10
Purchase #7	$175.30	9.274%	$191.5573	$191.56	$191.55	$191.60
7 purchase totals =	$757.81		$830.9696	$830.98	$830.95	$830.90