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	$170.57	10.314%	$188.1626	$188.16	$188.15	$188.20
Purchase #2	$109.47	6.812%	$116.9271	$116.93	$116.95	$116.90
Purchase #3	$139.92	9.575%	$153.3173	$153.32	$153.30	$153.30
Purchase #4	$94.26	11.351%	$104.9595	$104.96	$104.95	$105.00
Purchase #5	$198.31	13.409%	$224.9014	$224.90	$224.90	$224.90
Purchase #6	$43.37	5.113%	$45.5875	$45.59	$45.60	$45.60
Purchase #7	$143.83	10.509%	$158.9451	$158.95	$158.95	$158.90
7 purchase totals =	$899.73		$992.8005	$992.81	$992.80	$992.80