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	$225.29	6.530%	$240.0014	$240.00	$240.00	$240.00
Purchase #2	$230.76	4.778%	$241.7857	$241.79	$241.80	$241.80
Purchase #3	$92.69	11.670%	$103.5069	$103.51	$103.50	$103.50
Purchase #4	$137.52	3.481%	$142.3071	$142.31	$142.30	$142.30
Purchase #5	$91.34	7.817%	$98.48	$98.48	$98.50	$98.50
Purchase #6	$129.30	9.396%	$141.449	$141.45	$141.45	$141.40
Purchase #7	$72.49	6.262%	$77.0293	$77.03	$77.05	$77.00
7 purchase totals =	$979.39		$1,044.5594	$1,044.57	$1,044.60	$1,044.50