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	$53.51	3.303%	$55.2774	$55.28	$55.30	$55.30
Purchase #2	$119.80	8.547%	$130.0393	$130.04	$130.05	$130.00
Purchase #3	$55.68	10.285%	$61.4067	$61.41	$61.40	$61.40
Purchase #4	$150.31	6.321%	$159.8111	$159.81	$159.80	$159.80
Purchase #5	$163.42	13.206%	$185.0012	$185.00	$185.00	$185.00
Purchase #6	$127.64	5.191%	$134.2658	$134.27	$134.25	$134.30
Purchase #7	$71.60	9.348%	$78.2932	$78.29	$78.30	$78.30
7 purchase totals =	$741.96		$804.0947	$804.10	$804.10	$804.10