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	$144.80	12.493%	$162.8899	$162.89	$162.90	$162.90
Purchase #2	$112.84	6.404%	$120.0663	$120.07	$120.05	$120.10
Purchase #3	$77.87	7.447%	$83.669	$83.67	$83.65	$83.70
Purchase #4	$133.94	4.102%	$139.4342	$139.43	$139.45	$139.40
Purchase #5	$173.88	12.874%	$196.2653	$196.27	$196.25	$196.30
Purchase #6	$73.41	10.766%	$81.3133	$81.31	$81.30	$81.30
Purchase #7	$59.98	10.616%	$66.3475	$66.35	$66.35	$66.30
7 purchase totals =	$776.72		$849.9855	$849.99	$849.95	$850.00