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	$83.65	8.681%	$90.9117	$90.91	$90.90	$90.90
Purchase #2	$104.48	4.223%	$108.8922	$108.89	$108.90	$108.90
Purchase #3	$245.26	8.862%	$266.9949	$266.99	$267.00	$267.00
Purchase #4	$44.59	4.106%	$46.4209	$46.42	$46.40	$46.40
Purchase #5	$209.83	10.219%	$231.2725	$231.27	$231.25	$231.30
Purchase #6	$196.44	12.594%	$221.1797	$221.18	$221.20	$221.20
Purchase #7	$204.83	12.499%	$230.4317	$230.43	$230.45	$230.40
7 purchase totals =	$1,089.08		$1,196.1036	$1,196.09	$1,196.10	$1,196.10