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	$66.84	13.567%	$75.9082	$75.91	$75.90	$75.90
Purchase #2	$183.26	7.248%	$196.5427	$196.54	$196.55	$196.50
Purchase #3	$94.39	9.149%	$103.0257	$103.03	$103.05	$103.00
Purchase #4	$180.86	13.678%	$205.598	$205.60	$205.60	$205.60
Purchase #5	$151.60	4.483%	$158.3962	$158.40	$158.40	$158.40
Purchase #6	$78.82	9.324%	$86.1692	$86.17	$86.15	$86.20
Purchase #7	$61.81	7.103%	$66.2004	$66.20	$66.20	$66.20
7 purchase totals =	$817.58		$891.8404	$891.85	$891.85	$891.80