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	$24.92	11.693%	$27.8339	$27.83	$27.85	$27.80
Purchase #2	$85.94	8.125%	$92.9226	$92.92	$92.90	$92.90
Purchase #3	$151.46	13.694%	$172.2009	$172.20	$172.20	$172.20
Purchase #4	$81.59	13.848%	$92.8886	$92.89	$92.90	$92.90
Purchase #5	$175.84	11.652%	$196.3289	$196.33	$196.35	$196.30
Purchase #6	$16.77	13.233%	$18.9892	$18.99	$19.00	$19.00
Purchase #7	$176.39	10.810%	$195.4578	$195.46	$195.45	$195.50
7 purchase totals =	$712.91		$796.6219	$796.62	$796.65	$796.60