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	$77.62	10.136%	$85.4876	$85.49	$85.50	$85.50
Purchase #2	$37.76	12.652%	$42.5374	$42.54	$42.55	$42.50
Purchase #3	$98.86	3.775%	$102.592	$102.59	$102.60	$102.60
Purchase #4	$152.51	4.131%	$158.8102	$158.81	$158.80	$158.80
Purchase #5	$9.81	10.450%	$10.8351	$10.84	$10.85	$10.80
Purchase #6	$229.78	12.238%	$257.9005	$257.90	$257.90	$257.90
Purchase #7	$144.51	10.327%	$159.4335	$159.43	$159.45	$159.40
7 purchase totals =	$750.85		$817.5963	$817.60	$817.65	$817.50