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	$51.66	6.118%	$54.8206	$54.82	$54.80	$54.80
Purchase #2	$12.45	13.188%	$14.0919	$14.09	$14.10	$14.10
Purchase #3	$137.88	5.802%	$145.8798	$145.88	$145.90	$145.90
Purchase #4	$54.31	8.845%	$59.1137	$59.11	$59.10	$59.10
Purchase #5	$37.28	5.827%	$39.4523	$39.45	$39.45	$39.50
Purchase #6	$24.75	10.530%	$27.3562	$27.36	$27.35	$27.40
Purchase #7	$40.69	13.676%	$46.2548	$46.25	$46.25	$46.30
7 purchase totals =	$359.02		$386.9693	$386.96	$386.95	$387.10