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	$49.85	6.586%	$53.1331	$53.13	$53.15	$53.10
Purchase #2	$42.29	7.128%	$45.3044	$45.30	$45.30	$45.30
Purchase #3	$9.40	11.472%	$10.4784	$10.48	$10.50	$10.50
Purchase #4	$142.85	5.310%	$150.4353	$150.44	$150.45	$150.40
Purchase #5	$30.60	7.563%	$32.9143	$32.91	$32.90	$32.90
Purchase #6	$173.66	9.632%	$190.3869	$190.39	$190.40	$190.40
Purchase #7	$154.70	8.465%	$167.7954	$167.80	$167.80	$167.80
7 purchase totals =	$603.35		$650.4478	$650.45	$650.50	$650.40