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	$207.65	6.233%	$220.5928	$220.59	$220.60	$220.60
Purchase #2	$107.74	6.598%	$114.8487	$114.85	$114.85	$114.80
Purchase #3	$115.52	6.658%	$123.2113	$123.21	$123.20	$123.20
Purchase #4	$152.38	4.126%	$158.6672	$158.67	$158.65	$158.70
Purchase #5	$81.29	4.436%	$84.896	$84.90	$84.90	$84.90
Purchase #6	$94.58	11.496%	$105.4529	$105.45	$105.45	$105.50
Purchase #7	$37.25	13.625%	$42.3253	$42.33	$42.35	$42.30
7 purchase totals =	$796.41		$849.9942	$850.00	$850.00	$850.00