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	$72.81	9.299%	$79.5806	$79.58	$79.60	$79.60
Purchase #2	$178.27	11.127%	$198.1061	$198.11	$198.10	$198.10
Purchase #3	$132.66	9.506%	$145.2707	$145.27	$145.25	$145.30
Purchase #4	$24.63	10.305%	$27.1681	$27.17	$27.15	$27.20
Purchase #5	$143.67	11.790%	$160.6087	$160.61	$160.60	$160.60
Purchase #6	$153.49	8.699%	$166.8421	$166.84	$166.85	$166.80
Purchase #7	$85.70	4.869%	$89.8727	$89.87	$89.85	$89.90
7 purchase totals =	$791.23		$867.4490	$867.45	$867.40	$867.50