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	$167.99	9.603%	$184.1221	$184.12	$184.10	$184.10
Purchase #2	$227.47	5.629%	$240.2743	$240.27	$240.25	$240.30
Purchase #3	$122.75	13.621%	$139.4698	$139.47	$139.45	$139.50
Purchase #4	$134.46	10.523%	$148.6092	$148.61	$148.60	$148.60
Purchase #5	$165.59	4.616%	$173.2336	$173.23	$173.25	$173.20
Purchase #6	$151.80	9.743%	$166.5899	$166.59	$166.60	$166.60
Purchase #7	$130.35	12.611%	$146.7884	$146.79	$146.80	$146.80
7 purchase totals =	$1,100.41		$1,199.0873	$1,199.08	$1,199.05	$1,199.10