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	$160.29	3.213%	$165.4401	$165.44	$165.45	$165.40
Purchase #2	$39.51	8.535%	$42.8822	$42.88	$42.90	$42.90
Purchase #3	$227.74	10.765%	$252.2562	$252.26	$252.25	$252.30
Purchase #4	$11.42	11.713%	$12.7576	$12.76	$12.75	$12.80
Purchase #5	$48.60	5.804%	$51.4207	$51.42	$51.40	$51.40
Purchase #6	$83.49	8.869%	$90.8947	$90.89	$90.90	$90.90
Purchase #7	$190.40	8.122%	$205.8643	$205.86	$205.85	$205.90
7 purchase totals =	$761.45		$821.5158	$821.51	$821.50	$821.60