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	$152.65	3.177%	$157.4997	$157.50	$157.50	$157.50
Purchase #2	$43.97	4.680%	$46.0278	$46.03	$46.05	$46.00
Purchase #3	$130.60	11.480%	$145.5929	$145.59	$145.60	$145.60
Purchase #4	$175.56	6.422%	$186.8345	$186.83	$186.85	$186.80
Purchase #5	$114.98	11.390%	$128.0762	$128.08	$128.10	$128.10
Purchase #6	$196.80	9.428%	$215.3543	$215.35	$215.35	$215.40
Purchase #7	$245.94	11.468%	$274.1444	$274.14	$274.15	$274.10
7 purchase totals =	$1,060.50		$1,153.5298	$1,153.52	$1,153.60	$1,153.50