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	$14.86	6.623%	$15.8442	$15.84	$15.85	$15.80
Purchase #2	$64.49	12.134%	$72.3152	$72.32	$72.30	$72.30
Purchase #3	$72.47	10.808%	$80.3026	$80.30	$80.30	$80.30
Purchase #4	$154.85	12.619%	$174.3905	$174.39	$174.40	$174.40
Purchase #5	$122.25	8.849%	$133.0679	$133.07	$133.05	$133.10
Purchase #6	$204.50	9.337%	$223.5942	$223.59	$223.60	$223.60
Purchase #7	$57.30	9.313%	$62.6363	$62.64	$62.65	$62.60
7 purchase totals =	$690.72		$762.1509	$762.15	$762.15	$762.10