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	$68.37	6.163%	$72.5836	$72.58	$72.60	$72.60
Purchase #2	$131.50	13.141%	$148.7804	$148.78	$148.80	$148.80
Purchase #3	$75.43	4.622%	$78.9164	$78.92	$78.90	$78.90
Purchase #4	$228.63	11.505%	$254.9339	$254.93	$254.95	$254.90
Purchase #5	$109.34	12.208%	$122.6882	$122.69	$122.70	$122.70
Purchase #6	$64.68	9.537%	$70.8485	$70.85	$70.85	$70.80
Purchase #7	$175.86	5.619%	$185.7416	$185.74	$185.75	$185.70
7 purchase totals =	$853.81		$934.4926	$934.49	$934.55	$934.40