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	$74.66	6.702%	$79.6637	$79.66	$79.65	$79.70
Purchase #2	$210.79	3.223%	$217.5838	$217.58	$217.60	$217.60
Purchase #3	$149.74	5.328%	$157.7181	$157.72	$157.70	$157.70
Purchase #4	$143.91	8.581%	$156.2589	$156.26	$156.25	$156.30
Purchase #5	$62.96	6.451%	$67.0215	$67.02	$67.00	$67.00
Purchase #6	$214.83	3.188%	$221.6788	$221.68	$221.70	$221.70
Purchase #7	$72.30	8.637%	$78.5446	$78.54	$78.55	$78.50
7 purchase totals =	$929.19		$978.4694	$978.46	$978.45	$978.50