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	$36.97	10.480%	$40.8445	$40.84	$40.85	$40.80
Purchase #2	$66.76	10.844%	$73.9995	$74.00	$74.00	$74.00
Purchase #3	$145.63	11.808%	$162.826	$162.83	$162.85	$162.80
Purchase #4	$38.78	9.509%	$42.4676	$42.47	$42.45	$42.50
Purchase #5	$225.61	6.371%	$239.9836	$239.98	$240.00	$240.00
Purchase #6	$77.77	9.401%	$85.0812	$85.08	$85.10	$85.10
Purchase #7	$106.73	4.200%	$111.2127	$111.21	$111.20	$111.20
7 purchase totals =	$698.25		$756.4151	$756.41	$756.45	$756.40