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	$19.32	7.265%	$20.7236	$20.72	$20.70	$20.70
Purchase #2	$18.38	10.531%	$20.3156	$20.32	$20.30	$20.30
Purchase #3	$12.46	4.861%	$13.0657	$13.07	$13.05	$13.10
Purchase #4	$66.54	5.239%	$70.026	$70.03	$70.05	$70.00
Purchase #5	$78.58	9.520%	$86.0608	$86.06	$86.05	$86.10
Purchase #6	$112.41	13.664%	$127.7697	$127.77	$127.75	$127.80
Purchase #7	$126.25	13.523%	$143.3228	$143.32	$143.30	$143.30
7 purchase totals =	$433.94		$481.2842	$481.29	$481.20	$481.30