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	$49.32	4.296%	$51.4388	$51.44	$51.45	$51.40
Purchase #2	$91.70	8.595%	$99.5816	$99.58	$99.60	$99.60
Purchase #3	$83.83	3.285%	$86.5838	$86.58	$86.60	$86.60
Purchase #4	$195.57	9.503%	$214.155	$214.16	$214.15	$214.20
Purchase #5	$122.46	13.198%	$138.6223	$138.62	$138.60	$138.60
Purchase #6	$114.40	11.801%	$127.9003	$127.90	$127.90	$127.90
Purchase #7	$64.94	8.810%	$70.6612	$70.66	$70.65	$70.70
7 purchase totals =	$722.22		$788.9430	$788.94	$788.95	$789.00