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	$149.29	9.784%	$163.8965	$163.90	$163.90	$163.90
Purchase #2	$159.26	4.763%	$166.8456	$166.85	$166.85	$166.80
Purchase #3	$38.60	5.750%	$40.8195	$40.82	$40.80	$40.80
Purchase #4	$134.45	6.186%	$142.7671	$142.77	$142.75	$142.80
Purchase #5	$79.87	12.734%	$90.0406	$90.04	$90.05	$90.00
Purchase #6	$145.74	5.608%	$153.9131	$153.91	$153.90	$153.90
Purchase #7	$83.61	7.314%	$89.7252	$89.73	$89.75	$89.70
7 purchase totals =	$790.82		$848.0076	$848.02	$848.00	$847.90