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	$74.51	9.536%	$81.6153	$81.62	$81.60	$81.60
Purchase #2	$23.30	10.773%	$25.8101	$25.81	$25.80	$25.80
Purchase #3	$129.28	11.871%	$144.6268	$144.63	$144.65	$144.60
Purchase #4	$160.93	11.551%	$179.519	$179.52	$179.50	$179.50
Purchase #5	$109.75	7.390%	$117.8605	$117.86	$117.85	$117.90
Purchase #6	$133.95	12.334%	$150.4714	$150.47	$150.45	$150.50
Purchase #7	$104.61	11.187%	$116.3127	$116.31	$116.30	$116.30
7 purchase totals =	$736.33		$816.2158	$816.22	$816.15	$816.20