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	$37.71	8.262%	$40.8256	$40.83	$40.85	$40.80
Purchase #2	$207.77	8.584%	$225.605	$225.61	$225.60	$225.60
Purchase #3	$182.38	9.240%	$199.2319	$199.23	$199.25	$199.20
Purchase #4	$116.84	4.798%	$122.446	$122.45	$122.45	$122.40
Purchase #5	$249.90	5.483%	$263.602	$263.60	$263.60	$263.60
Purchase #6	$240.75	10.260%	$265.451	$265.45	$265.45	$265.50
Purchase #7	$165.87	4.528%	$173.3806	$173.38	$173.40	$173.40
7 purchase totals =	$1,201.22		$1,290.5421	$1,290.55	$1,290.60	$1,290.50