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	$140.60	5.770%	$148.7126	$148.71	$148.70	$148.70
Purchase #2	$107.47	9.727%	$117.9236	$117.92	$117.90	$117.90
Purchase #3	$163.48	13.363%	$185.3258	$185.33	$185.35	$185.30
Purchase #4	$30.82	10.240%	$33.976	$33.98	$34.00	$34.00
Purchase #5	$121.87	12.771%	$137.434	$137.43	$137.45	$137.40
Purchase #6	$158.37	9.133%	$172.8339	$172.83	$172.85	$172.80
Purchase #7	$67.70	7.337%	$72.6671	$72.67	$72.65	$72.70
7 purchase totals =	$790.31		$868.8730	$868.87	$868.90	$868.80