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	$86.56	3.243%	$89.3671	$89.37	$89.35	$89.40
Purchase #2	$151.91	9.826%	$166.8367	$166.84	$166.85	$166.80
Purchase #3	$165.80	6.656%	$176.8356	$176.84	$176.85	$176.80
Purchase #4	$162.60	4.642%	$170.1479	$170.15	$170.15	$170.10
Purchase #5	$7.80	8.353%	$8.4515	$8.45	$8.45	$8.50
Purchase #6	$100.72	3.670%	$104.4164	$104.42	$104.40	$104.40
Purchase #7	$63.77	10.610%	$70.536	$70.54	$70.55	$70.50
7 purchase totals =	$739.16		$786.5912	$786.61	$786.60	$786.50