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	$32.50	3.385%	$33.6001	$33.60	$33.60	$33.60
Purchase #2	$75.81	3.269%	$78.2882	$78.29	$78.30	$78.30
Purchase #3	$121.59	5.865%	$128.7213	$128.72	$128.70	$128.70
Purchase #4	$179.95	10.365%	$198.6018	$198.60	$198.60	$198.60
Purchase #5	$22.45	12.102%	$25.1669	$25.17	$25.15	$25.20
Purchase #6	$146.34	3.379%	$151.2848	$151.28	$151.30	$151.30
Purchase #7	$21.55	8.204%	$23.318	$23.32	$23.30	$23.30
7 purchase totals =	$600.19		$638.9811	$638.98	$638.95	$639.00