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	$73.75	6.592%	$78.6116	$78.61	$78.60	$78.60
Purchase #2	$151.86	3.823%	$157.6656	$157.67	$157.65	$157.70
Purchase #3	$15.34	3.423%	$15.8651	$15.87	$15.85	$15.90
Purchase #4	$83.33	10.281%	$91.8972	$91.90	$91.90	$91.90
Purchase #5	$42.78	11.142%	$47.5465	$47.55	$47.55	$47.50
Purchase #6	$30.32	7.719%	$32.6604	$32.66	$32.65	$32.70
Purchase #7	$64.77	3.202%	$66.8439	$66.84	$66.85	$66.80
7 purchase totals =	$462.15		$491.0903	$491.10	$491.05	$491.10