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	$164.88	12.783%	$185.9566	$185.96	$185.95	$186.00
Purchase #2	$125.91	12.565%	$141.7306	$141.73	$141.75	$141.70
Purchase #3	$100.90	11.209%	$112.2099	$112.21	$112.20	$112.20
Purchase #4	$159.82	8.533%	$173.4574	$173.46	$173.45	$173.50
Purchase #5	$57.54	5.636%	$60.783	$60.78	$60.80	$60.80
Purchase #6	$246.72	12.493%	$277.5427	$277.54	$277.55	$277.50
Purchase #7	$77.78	12.456%	$87.4683	$87.47	$87.45	$87.50
7 purchase totals =	$933.55		$1,039.1485	$1,039.15	$1,039.15	$1,039.20