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	$50.61	13.188%	$57.2844	$57.28	$57.30	$57.30
Purchase #2	$178.72	3.852%	$185.6043	$185.60	$185.60	$185.60
Purchase #3	$20.78	13.250%	$23.5334	$23.53	$23.55	$23.50
Purchase #4	$155.49	7.605%	$167.315	$167.32	$167.30	$167.30
Purchase #5	$220.59	4.364%	$230.2165	$230.22	$230.20	$230.20
Purchase #6	$160.30	5.749%	$169.5156	$169.52	$169.50	$169.50
Purchase #7	$71.27	9.737%	$78.2096	$78.21	$78.20	$78.20
7 purchase totals =	$857.76		$911.6788	$911.68	$911.65	$911.60