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	$70.89	10.246%	$78.1534	$78.15	$78.15	$78.20
Purchase #2	$184.34	3.222%	$190.2794	$190.28	$190.30	$190.30
Purchase #3	$204.58	10.330%	$225.7131	$225.71	$225.70	$225.70
Purchase #4	$165.51	4.737%	$173.3502	$173.35	$173.35	$173.40
Purchase #5	$74.63	5.278%	$78.569	$78.57	$78.55	$78.60
Purchase #6	$158.34	11.549%	$176.6267	$176.63	$176.65	$176.60
Purchase #7	$82.67	7.538%	$88.9017	$88.90	$88.90	$88.90
7 purchase totals =	$940.96		$1,011.5935	$1,011.59	$1,011.60	$1,011.70