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	$126.37	11.723%	$141.1844	$141.18	$141.20	$141.20
Purchase #2	$69.78	3.491%	$72.216	$72.22	$72.20	$72.20
Purchase #3	$241.54	3.861%	$250.8659	$250.87	$250.85	$250.90
Purchase #4	$59.92	4.439%	$62.5798	$62.58	$62.60	$62.60
Purchase #5	$53.50	6.276%	$56.8577	$56.86	$56.85	$56.90
Purchase #6	$240.90	8.796%	$262.0896	$262.09	$262.10	$262.10
Purchase #7	$11.51	12.571%	$12.9569	$12.96	$12.95	$13.00
7 purchase totals =	$803.52		$858.7503	$858.76	$858.75	$858.90