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	$234.85	6.675%	$250.5262	$250.53	$250.55	$250.50
Purchase #2	$216.74	9.722%	$237.8115	$237.81	$237.80	$237.80
Purchase #3	$172.46	13.750%	$196.1733	$196.17	$196.15	$196.20
Purchase #4	$172.64	8.783%	$187.803	$187.80	$187.80	$187.80
Purchase #5	$30.56	7.361%	$32.8095	$32.81	$32.80	$32.80
Purchase #6	$146.50	3.186%	$151.1675	$151.17	$151.15	$151.20
Purchase #7	$12.80	4.667%	$13.3974	$13.40	$13.40	$13.40
7 purchase totals =	$986.55		$1,069.6884	$1,069.69	$1,069.65	$1,069.70