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	$125.80	3.803%	$130.5842	$130.58	$130.60	$130.60
Purchase #2	$31.89	7.834%	$34.3883	$34.39	$34.40	$34.40
Purchase #3	$92.48	12.377%	$103.9262	$103.93	$103.95	$103.90
Purchase #4	$143.49	6.718%	$153.1297	$153.13	$153.15	$153.10
Purchase #5	$125.77	9.529%	$137.7546	$137.75	$137.75	$137.80
Purchase #6	$137.25	12.645%	$154.6053	$154.61	$154.60	$154.60
Purchase #7	$230.54	10.788%	$255.4107	$255.41	$255.40	$255.40
7 purchase totals =	$887.22		$969.7990	$969.80	$969.85	$969.80