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	$87.43	13.829%	$99.5207	$99.52	$99.50	$99.50
Purchase #2	$174.26	6.295%	$185.2297	$185.23	$185.25	$185.20
Purchase #3	$165.65	4.611%	$173.2881	$173.29	$173.30	$173.30
Purchase #4	$156.33	11.763%	$174.7191	$174.72	$174.70	$174.70
Purchase #5	$161.63	6.325%	$171.8531	$171.85	$171.85	$171.90
Purchase #6	$154.48	10.162%	$170.1783	$170.18	$170.20	$170.20
Purchase #7	$33.40	3.618%	$34.6084	$34.61	$34.60	$34.60
7 purchase totals =	$933.18		$1,009.3974	$1,009.40	$1,009.40	$1,009.40