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	$235.99	8.232%	$255.4167	$255.42	$255.40	$255.40
Purchase #2	$228.47	6.558%	$243.4531	$243.45	$243.45	$243.50
Purchase #3	$78.86	4.348%	$82.2888	$82.29	$82.30	$82.30
Purchase #4	$240.98	5.380%	$253.9447	$253.94	$253.95	$253.90
Purchase #5	$245.95	8.764%	$267.5051	$267.51	$267.50	$267.50
Purchase #6	$96.46	12.158%	$108.1876	$108.19	$108.20	$108.20
Purchase #7	$69.35	10.712%	$76.7788	$76.78	$76.80	$76.80
7 purchase totals =	$1,196.06		$1,287.5748	$1,287.58	$1,287.60	$1,287.60