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	$177.40	6.356%	$188.6755	$188.68	$188.70	$188.70
Purchase #2	$173.27	8.584%	$188.1435	$188.14	$188.15	$188.10
Purchase #3	$164.28	6.127%	$174.3454	$174.35	$174.35	$174.30
Purchase #4	$53.59	3.451%	$55.4394	$55.44	$55.45	$55.40
Purchase #5	$28.72	13.432%	$32.5777	$32.58	$32.60	$32.60
Purchase #6	$68.85	12.158%	$77.2208	$77.22	$77.20	$77.20
Purchase #7	$141.78	7.167%	$151.9414	$151.94	$151.95	$151.90
7 purchase totals =	$807.89		$868.3437	$868.35	$868.40	$868.20