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	$145.88	13.870%	$166.1136	$166.11	$166.10	$166.10
Purchase #2	$152.82	12.486%	$171.9011	$171.90	$171.90	$171.90
Purchase #3	$100.98	3.621%	$104.6365	$104.64	$104.65	$104.60
Purchase #4	$86.58	8.762%	$94.1661	$94.17	$94.15	$94.20
Purchase #5	$128.27	12.125%	$143.8227	$143.82	$143.80	$143.80
Purchase #6	$158.28	11.327%	$176.2084	$176.21	$176.20	$176.20
Purchase #7	$230.78	5.205%	$242.7921	$242.79	$242.80	$242.80
7 purchase totals =	$1,003.59		$1,099.6405	$1,099.64	$1,099.60	$1,099.60