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	$23.27	3.163%	$24.006	$24.01	$24.00	$24.00
Purchase #2	$125.70	4.697%	$131.6041	$131.60	$131.60	$131.60
Purchase #3	$123.56	12.770%	$139.3386	$139.34	$139.35	$139.30
Purchase #4	$85.70	5.737%	$90.6166	$90.62	$90.60	$90.60
Purchase #5	$161.74	6.451%	$172.1738	$172.17	$172.15	$172.20
Purchase #6	$25.94	9.191%	$28.3241	$28.32	$28.30	$28.30
Purchase #7	$145.82	10.809%	$161.5817	$161.58	$161.60	$161.60
7 purchase totals =	$691.73		$747.6449	$747.64	$747.60	$747.60