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	$240.26	12.208%	$269.5909	$269.59	$269.60	$269.60
Purchase #2	$13.79	12.856%	$15.5628	$15.56	$15.55	$15.60
Purchase #3	$116.71	3.132%	$120.3654	$120.37	$120.35	$120.40
Purchase #4	$81.91	9.471%	$89.6677	$89.67	$89.65	$89.70
Purchase #5	$132.37	5.619%	$139.8079	$139.81	$139.80	$139.80
Purchase #6	$9.60	9.576%	$10.5193	$10.52	$10.50	$10.50
Purchase #7	$153.32	12.609%	$172.6521	$172.65	$172.65	$172.70
7 purchase totals =	$747.96		$818.1661	$818.17	$818.10	$818.30