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	$22.76	4.861%	$23.8664	$23.87	$23.85	$23.90
Purchase #2	$117.72	11.152%	$130.8481	$130.85	$130.85	$130.80
Purchase #3	$73.54	7.174%	$78.8158	$78.82	$78.80	$78.80
Purchase #4	$69.37	13.785%	$78.9327	$78.93	$78.95	$78.90
Purchase #5	$100.59	5.322%	$105.9434	$105.94	$105.95	$105.90
Purchase #6	$10.43	8.407%	$11.3069	$11.31	$11.30	$11.30
Purchase #7	$26.59	11.229%	$29.5758	$29.58	$29.60	$29.60
7 purchase totals =	$421.00		$459.2891	$459.30	$459.30	$459.20