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	$244.34	6.116%	$259.2838	$259.28	$259.30	$259.30
Purchase #2	$172.73	10.265%	$190.4607	$190.46	$190.45	$190.50
Purchase #3	$99.70	8.874%	$108.5474	$108.55	$108.55	$108.50
Purchase #4	$215.37	3.760%	$223.4679	$223.47	$223.45	$223.50
Purchase #5	$216.52	5.347%	$228.0973	$228.10	$228.10	$228.10
Purchase #6	$21.81	10.691%	$24.1417	$24.14	$24.15	$24.10
Purchase #7	$172.62	3.466%	$178.603	$178.60	$178.60	$178.60
7 purchase totals =	$1,143.09		$1,212.6018	$1,212.60	$1,212.60	$1,212.60