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	$138.66	3.795%	$143.9221	$143.92	$143.90	$143.90
Purchase #2	$152.26	4.299%	$158.8057	$158.81	$158.80	$158.80
Purchase #3	$145.65	8.143%	$157.5103	$157.51	$157.50	$157.50
Purchase #4	$173.89	7.859%	$187.556	$187.56	$187.55	$187.60
Purchase #5	$233.38	9.323%	$255.138	$255.14	$255.15	$255.10
Purchase #6	$247.94	12.308%	$278.4565	$278.46	$278.45	$278.50
Purchase #7	$167.68	7.394%	$180.0783	$180.08	$180.10	$180.10
7 purchase totals =	$1,259.46		$1,361.4669	$1,361.48	$1,361.45	$1,361.50