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	$38.96	12.378%	$43.7825	$43.78	$43.80	$43.80
Purchase #2	$204.77	12.762%	$230.9027	$230.90	$230.90	$230.90
Purchase #3	$15.65	12.338%	$17.5809	$17.58	$17.60	$17.60
Purchase #4	$67.72	5.327%	$71.3274	$71.33	$71.35	$71.30
Purchase #5	$64.88	13.248%	$73.4753	$73.48	$73.50	$73.50
Purchase #6	$197.89	5.502%	$208.7779	$208.78	$208.80	$208.80
Purchase #7	$142.49	6.308%	$151.4783	$151.48	$151.50	$151.50
7 purchase totals =	$732.36		$797.3250	$797.33	$797.45	$797.40