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	$20.53	6.434%	$21.8509	$21.85	$21.85	$21.90
Purchase #2	$196.65	13.712%	$223.6146	$223.61	$223.60	$223.60
Purchase #3	$16.73	5.364%	$17.6274	$17.63	$17.65	$17.60
Purchase #4	$56.89	10.862%	$63.0694	$63.07	$63.05	$63.10
Purchase #5	$40.86	12.302%	$45.8866	$45.89	$45.90	$45.90
Purchase #6	$65.44	12.339%	$73.5146	$73.51	$73.50	$73.50
Purchase #7	$167.43	3.391%	$173.1076	$173.11	$173.10	$173.10
7 purchase totals =	$564.53		$618.6711	$618.67	$618.65	$618.70