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	$172.35	6.236%	$183.0977	$183.10	$183.10	$183.10
Purchase #2	$190.34	4.335%	$198.5912	$198.59	$198.60	$198.60
Purchase #3	$206.92	7.615%	$222.677	$222.68	$222.70	$222.70
Purchase #4	$223.94	3.454%	$231.6749	$231.67	$231.65	$231.70
Purchase #5	$36.83	7.435%	$39.5683	$39.57	$39.55	$39.60
Purchase #6	$59.42	13.477%	$67.428	$67.43	$67.45	$67.40
Purchase #7	$132.92	7.832%	$143.3303	$143.33	$143.35	$143.30
7 purchase totals =	$1,022.72		$1,086.3674	$1,086.37	$1,086.40	$1,086.40