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	$33.44	11.153%	$37.1696	$37.17	$37.15	$37.20
Purchase #2	$157.29	9.586%	$172.3678	$172.37	$172.35	$172.40
Purchase #3	$128.45	9.477%	$140.6232	$140.62	$140.60	$140.60
Purchase #4	$155.96	11.419%	$173.7691	$173.77	$173.75	$173.80
Purchase #5	$79.63	12.588%	$89.6538	$89.65	$89.65	$89.70
Purchase #6	$169.36	3.163%	$174.7169	$174.72	$174.70	$174.70
Purchase #7	$152.87	12.778%	$172.4037	$172.40	$172.40	$172.40
7 purchase totals =	$877.00		$960.7041	$960.70	$960.60	$960.80