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	$155.66	6.591%	$165.9196	$165.92	$165.90	$165.90
Purchase #2	$37.68	3.535%	$39.012	$39.01	$39.00	$39.00
Purchase #3	$122.62	6.417%	$130.4885	$130.49	$130.50	$130.50
Purchase #4	$105.49	5.683%	$111.485	$111.49	$111.50	$111.50
Purchase #5	$71.34	9.472%	$78.0973	$78.10	$78.10	$78.10
Purchase #6	$35.45	6.271%	$37.6731	$37.67	$37.65	$37.70
Purchase #7	$14.66	13.346%	$16.6165	$16.62	$16.60	$16.60
7 purchase totals =	$542.90		$579.2920	$579.30	$579.25	$579.30