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	$49.81	9.378%	$54.4812	$54.48	$54.50	$54.50
Purchase #2	$71.42	6.243%	$75.8788	$75.88	$75.90	$75.90
Purchase #3	$160.76	7.641%	$173.0437	$173.04	$173.05	$173.00
Purchase #4	$242.60	8.252%	$262.6194	$262.62	$262.60	$262.60
Purchase #5	$102.33	8.788%	$111.3228	$111.32	$111.30	$111.30
Purchase #6	$233.39	12.590%	$262.7738	$262.77	$262.75	$262.80
Purchase #7	$45.47	10.646%	$50.3107	$50.31	$50.30	$50.30
7 purchase totals =	$905.78		$990.4304	$990.42	$990.40	$990.40