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	$108.31	12.363%	$121.7004	$121.70	$121.70	$121.70
Purchase #2	$140.92	3.327%	$145.6084	$145.61	$145.60	$145.60
Purchase #3	$156.55	5.144%	$164.6029	$164.60	$164.60	$164.60
Purchase #4	$8.96	13.301%	$10.1518	$10.15	$10.15	$10.20
Purchase #5	$158.52	4.582%	$165.7834	$165.78	$165.80	$165.80
Purchase #6	$154.89	7.393%	$166.341	$166.34	$166.35	$166.30
Purchase #7	$142.28	9.820%	$156.2519	$156.25	$156.25	$156.30
7 purchase totals =	$870.43		$930.4398	$930.43	$930.45	$930.50