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	$24.40	12.592%	$27.4724	$27.47	$27.45	$27.50
Purchase #2	$127.68	13.662%	$145.1236	$145.12	$145.10	$145.10
Purchase #3	$67.49	7.495%	$72.5484	$72.55	$72.55	$72.50
Purchase #4	$104.29	12.114%	$116.9237	$116.92	$116.90	$116.90
Purchase #5	$133.51	9.865%	$146.6808	$146.68	$146.70	$146.70
Purchase #6	$114.99	7.437%	$123.5418	$123.54	$123.55	$123.50
Purchase #7	$17.49	6.723%	$18.6659	$18.67	$18.65	$18.70
7 purchase totals =	$589.85		$650.9566	$650.95	$650.90	$650.90