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	$25.90	11.236%	$28.8101	$28.81	$28.80	$28.80
Purchase #2	$172.60	13.844%	$196.4947	$196.49	$196.50	$196.50
Purchase #3	$151.46	6.257%	$160.9369	$160.94	$160.95	$160.90
Purchase #4	$183.51	4.512%	$191.79	$191.79	$191.80	$191.80
Purchase #5	$10.99	10.276%	$12.1193	$12.12	$12.10	$12.10
Purchase #6	$59.89	11.194%	$66.5941	$66.59	$66.60	$66.60
Purchase #7	$205.65	10.837%	$227.9363	$227.94	$227.95	$227.90
7 purchase totals =	$810.00		$884.6814	$884.68	$884.70	$884.60