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	$15.94	8.394%	$17.278	$17.28	$17.30	$17.30
Purchase #2	$52.59	7.671%	$56.6242	$56.62	$56.60	$56.60
Purchase #3	$36.38	9.409%	$39.803	$39.80	$39.80	$39.80
Purchase #4	$141.46	6.855%	$151.1571	$151.16	$151.15	$151.20
Purchase #5	$188.28	4.122%	$196.0409	$196.04	$196.05	$196.00
Purchase #6	$38.46	11.122%	$42.7375	$42.74	$42.75	$42.70
Purchase #7	$92.92	9.403%	$101.6573	$101.66	$101.65	$101.70
7 purchase totals =	$566.03		$605.2980	$605.30	$605.30	$605.30