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	$68.28	9.628%	$74.854	$74.85	$74.85	$74.90
Purchase #2	$71.90	7.622%	$77.3802	$77.38	$77.40	$77.40
Purchase #3	$74.96	4.546%	$78.3677	$78.37	$78.35	$78.40
Purchase #4	$78.87	12.335%	$88.5986	$88.60	$88.60	$88.60
Purchase #5	$151.45	9.799%	$166.2906	$166.29	$166.30	$166.30
Purchase #6	$31.47	5.511%	$33.2043	$33.20	$33.20	$33.20
Purchase #7	$244.81	6.457%	$260.6174	$260.62	$260.60	$260.60
7 purchase totals =	$721.74		$779.3128	$779.31	$779.30	$779.40