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	$31.83	6.388%	$33.8633	$33.86	$33.85	$33.90
Purchase #2	$145.36	12.838%	$164.0213	$164.02	$164.00	$164.00
Purchase #3	$104.85	6.337%	$111.4943	$111.49	$111.50	$111.50
Purchase #4	$38.49	6.821%	$41.1154	$41.12	$41.10	$41.10
Purchase #5	$203.36	5.546%	$214.6383	$214.64	$214.65	$214.60
Purchase #6	$14.87	4.437%	$15.5298	$15.53	$15.55	$15.50
Purchase #7	$222.40	8.118%	$240.4544	$240.45	$240.45	$240.50
7 purchase totals =	$761.16		$821.1168	$821.11	$821.10	$821.10