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	$115.76	13.222%	$131.0658	$131.07	$131.05	$131.10
Purchase #2	$181.27	8.547%	$196.7631	$196.76	$196.75	$196.80
Purchase #3	$241.64	11.575%	$269.6098	$269.61	$269.60	$269.60
Purchase #4	$12.57	8.653%	$13.6577	$13.66	$13.65	$13.70
Purchase #5	$124.27	10.366%	$137.1518	$137.15	$137.15	$137.20
Purchase #6	$92.93	5.397%	$97.9454	$97.95	$97.95	$97.90
Purchase #7	$38.51	7.199%	$41.2823	$41.28	$41.30	$41.30
7 purchase totals =	$806.95		$887.4759	$887.48	$887.45	$887.60