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	$57.63	13.752%	$65.5553	$65.56	$65.55	$65.60
Purchase #2	$11.74	7.229%	$12.5887	$12.59	$12.60	$12.60
Purchase #3	$102.73	8.320%	$111.2771	$111.28	$111.30	$111.30
Purchase #4	$174.32	10.141%	$191.9978	$192.00	$192.00	$192.00
Purchase #5	$87.90	13.865%	$100.0873	$100.09	$100.10	$100.10
Purchase #6	$79.38	10.413%	$87.6458	$87.65	$87.65	$87.60
Purchase #7	$10.82	12.817%	$12.2068	$12.21	$12.20	$12.20
7 purchase totals =	$524.52		$581.3588	$581.38	$581.40	$581.40