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	$58.35	13.871%	$66.4437	$66.44	$66.45	$66.40
Purchase #2	$123.71	5.828%	$130.9198	$130.92	$130.90	$130.90
Purchase #3	$101.34	10.435%	$111.9148	$111.91	$111.90	$111.90
Purchase #4	$34.74	9.336%	$37.9833	$37.98	$38.00	$38.00
Purchase #5	$188.71	8.120%	$204.0333	$204.03	$204.05	$204.00
Purchase #6	$161.78	6.664%	$172.561	$172.56	$172.55	$172.60
Purchase #7	$87.55	10.859%	$97.0571	$97.06	$97.05	$97.10
7 purchase totals =	$756.18		$820.9130	$820.90	$820.90	$820.90