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	$106.67	10.212%	$117.5631	$117.56	$117.55	$117.60
Purchase #2	$166.46	11.230%	$185.1535	$185.15	$185.15	$185.20
Purchase #3	$132.53	8.217%	$143.42	$143.42	$143.40	$143.40
Purchase #4	$118.93	11.420%	$132.5118	$132.51	$132.50	$132.50
Purchase #5	$77.93	4.487%	$81.4267	$81.43	$81.45	$81.40
Purchase #6	$42.34	13.312%	$47.9763	$47.98	$48.00	$48.00
Purchase #7	$31.29	5.732%	$33.0835	$33.08	$33.10	$33.10
7 purchase totals =	$676.15		$741.1349	$741.13	$741.15	$741.20