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	$22.41	7.463%	$24.0825	$24.08	$24.10	$24.10
Purchase #2	$143.81	7.196%	$154.1586	$154.16	$154.15	$154.20
Purchase #3	$215.51	10.483%	$238.1019	$238.10	$238.10	$238.10
Purchase #4	$160.33	4.786%	$168.0034	$168.00	$168.00	$168.00
Purchase #5	$55.82	3.679%	$57.8736	$57.87	$57.85	$57.90
Purchase #6	$145.45	13.546%	$165.1527	$165.15	$165.15	$165.20
Purchase #7	$153.71	12.504%	$172.9299	$172.93	$172.95	$172.90
7 purchase totals =	$897.04		$980.3026	$980.29	$980.30	$980.40