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	$234.57	4.691%	$245.5737	$245.57	$245.55	$245.60
Purchase #2	$113.31	12.422%	$127.3854	$127.39	$127.40	$127.40
Purchase #3	$79.35	13.259%	$89.871	$89.87	$89.85	$89.90
Purchase #4	$173.50	3.747%	$180.001	$180.00	$180.00	$180.00
Purchase #5	$11.79	11.698%	$13.1692	$13.17	$13.15	$13.20
Purchase #6	$146.68	10.204%	$161.6472	$161.65	$161.65	$161.60
Purchase #7	$75.25	10.397%	$83.0737	$83.07	$83.05	$83.10
7 purchase totals =	$834.45		$900.7212	$900.72	$900.65	$900.80