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	$144.84	10.195%	$159.6064	$159.61	$159.60	$159.60
Purchase #2	$83.78	8.145%	$90.6039	$90.60	$90.60	$90.60
Purchase #3	$45.40	4.727%	$47.5461	$47.55	$47.55	$47.50
Purchase #4	$105.35	10.379%	$116.2843	$116.28	$116.30	$116.30
Purchase #5	$75.31	5.646%	$79.562	$79.56	$79.55	$79.60
Purchase #6	$159.51	11.581%	$177.9829	$177.98	$178.00	$178.00
Purchase #7	$162.71	7.832%	$175.4534	$175.45	$175.45	$175.50
7 purchase totals =	$776.90		$847.0390	$847.03	$847.05	$847.10