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	$85.65	4.703%	$89.6781	$89.68	$89.70	$89.70
Purchase #2	$145.87	8.189%	$157.8153	$157.82	$157.80	$157.80
Purchase #3	$96.59	10.187%	$106.4296	$106.43	$106.45	$106.40
Purchase #4	$95.47	8.224%	$103.3215	$103.32	$103.30	$103.30
Purchase #5	$170.86	12.410%	$192.0637	$192.06	$192.05	$192.10
Purchase #6	$119.40	3.491%	$123.5683	$123.57	$123.55	$123.60
Purchase #7	$74.45	9.227%	$81.3195	$81.32	$81.30	$81.30
7 purchase totals =	$788.29		$854.1960	$854.20	$854.15	$854.20