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	$39.88	3.723%	$41.3647	$41.36	$41.35	$41.40
Purchase #2	$61.75	6.352%	$65.6724	$65.67	$65.65	$65.70
Purchase #3	$117.54	11.653%	$131.2369	$131.24	$131.25	$131.20
Purchase #4	$51.41	4.226%	$53.5826	$53.58	$53.60	$53.60
Purchase #5	$32.39	10.757%	$35.8742	$35.87	$35.85	$35.90
Purchase #6	$122.59	6.147%	$130.1256	$130.13	$130.15	$130.10
Purchase #7	$216.85	3.806%	$225.1033	$225.10	$225.10	$225.10
7 purchase totals =	$642.41		$682.9597	$682.95	$682.95	$683.00