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	$250.28	8.485%	$271.5163	$271.52	$271.50	$271.50
Purchase #2	$8.29	5.750%	$8.7667	$8.77	$8.75	$8.80
Purchase #3	$96.82	9.326%	$105.8494	$105.85	$105.85	$105.80
Purchase #4	$220.93	4.630%	$231.1591	$231.16	$231.15	$231.20
Purchase #5	$62.82	4.758%	$65.809	$65.81	$65.80	$65.80
Purchase #6	$33.43	12.422%	$37.5827	$37.58	$37.60	$37.60
Purchase #7	$36.29	5.318%	$38.2199	$38.22	$38.20	$38.20
7 purchase totals =	$708.86		$758.9031	$758.91	$758.85	$758.90