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	$12.46	11.626%	$13.9086	$13.91	$13.90	$13.90
Purchase #2	$119.79	6.503%	$127.5799	$127.58	$127.60	$127.60
Purchase #3	$146.31	13.146%	$165.5439	$165.54	$165.55	$165.50
Purchase #4	$8.89	13.239%	$10.0669	$10.07	$10.05	$10.10
Purchase #5	$54.66	4.653%	$57.2033	$57.20	$57.20	$57.20
Purchase #6	$208.50	3.552%	$215.9059	$215.91	$215.90	$215.90
Purchase #7	$220.51	13.793%	$250.9249	$250.92	$250.90	$250.90
7 purchase totals =	$771.12		$841.1334	$841.13	$841.10	$841.10