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	$189.73	8.833%	$206.4889	$206.49	$206.50	$206.50
Purchase #2	$173.94	10.202%	$191.6854	$191.69	$191.70	$191.70
Purchase #3	$106.99	8.803%	$116.4083	$116.41	$116.40	$116.40
Purchase #4	$111.39	10.791%	$123.4101	$123.41	$123.40	$123.40
Purchase #5	$79.45	12.516%	$89.394	$89.39	$89.40	$89.40
Purchase #6	$12.94	5.188%	$13.6113	$13.61	$13.60	$13.60
Purchase #7	$167.59	4.483%	$175.1031	$175.10	$175.10	$175.10
7 purchase totals =	$842.03		$916.1011	$916.10	$916.10	$916.10