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	$180.50	5.471%	$190.3752	$190.38	$190.40	$190.40
Purchase #2	$67.44	6.429%	$71.7757	$71.78	$71.80	$71.80
Purchase #3	$136.70	4.515%	$142.872	$142.87	$142.85	$142.90
Purchase #4	$148.81	4.800%	$155.9529	$155.95	$155.95	$156.00
Purchase #5	$196.28	11.859%	$219.5568	$219.56	$219.55	$219.60
Purchase #6	$108.85	8.692%	$118.3112	$118.31	$118.30	$118.30
Purchase #7	$10.95	3.149%	$11.2948	$11.29	$11.30	$11.30
7 purchase totals =	$849.53		$910.1386	$910.14	$910.15	$910.30