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	$18.63	7.760%	$20.0757	$20.08	$20.10	$20.10
Purchase #2	$144.39	12.631%	$162.6279	$162.63	$162.65	$162.60
Purchase #3	$181.28	6.455%	$192.9816	$192.98	$193.00	$193.00
Purchase #4	$128.90	8.288%	$139.5832	$139.58	$139.60	$139.60
Purchase #5	$114.43	12.441%	$128.6662	$128.67	$128.65	$128.70
Purchase #6	$79.46	13.680%	$90.3301	$90.33	$90.35	$90.30
Purchase #7	$180.88	10.257%	$199.4329	$199.43	$199.45	$199.40
7 purchase totals =	$847.97		$933.6976	$933.70	$933.80	$933.70