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	$138.38	4.361%	$144.4148	$144.41	$144.40	$144.40
Purchase #2	$134.74	5.309%	$141.8933	$141.89	$141.90	$141.90
Purchase #3	$151.86	9.422%	$166.1682	$166.17	$166.15	$166.20
Purchase #4	$137.93	9.190%	$150.6058	$150.61	$150.60	$150.60
Purchase #5	$110.29	10.488%	$121.8572	$121.86	$121.85	$121.90
Purchase #6	$114.80	10.152%	$126.4545	$126.45	$126.45	$126.50
Purchase #7	$40.63	13.772%	$46.2256	$46.23	$46.25	$46.20
7 purchase totals =	$828.63		$897.6194	$897.62	$897.60	$897.70