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	$74.77	13.306%	$84.7189	$84.72	$84.70	$84.70
Purchase #2	$224.49	13.102%	$253.9027	$253.90	$253.90	$253.90
Purchase #3	$40.71	12.725%	$45.8903	$45.89	$45.90	$45.90
Purchase #4	$194.92	11.721%	$217.7666	$217.77	$217.75	$217.80
Purchase #5	$94.78	5.259%	$99.7645	$99.76	$99.75	$99.80
Purchase #6	$33.40	9.622%	$36.6137	$36.61	$36.60	$36.60
Purchase #7	$115.35	7.215%	$123.6725	$123.67	$123.65	$123.70
7 purchase totals =	$778.42		$862.3292	$862.32	$862.25	$862.40