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	$89.72	3.149%	$92.5453	$92.55	$92.55	$92.50
Purchase #2	$183.49	3.270%	$189.4901	$189.49	$189.50	$189.50
Purchase #3	$117.72	8.194%	$127.366	$127.37	$127.35	$127.40
Purchase #4	$21.32	3.693%	$22.1073	$22.11	$22.10	$22.10
Purchase #5	$71.48	9.139%	$78.0126	$78.01	$78.00	$78.00
Purchase #6	$34.26	11.629%	$38.2441	$38.24	$38.25	$38.20
Purchase #7	$51.51	9.873%	$56.5956	$56.60	$56.60	$56.60
7 purchase totals =	$569.50		$604.3610	$604.37	$604.35	$604.30