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	$35.70	9.593%	$39.1247	$39.12	$39.10	$39.10
Purchase #2	$13.27	6.425%	$14.1226	$14.12	$14.10	$14.10
Purchase #3	$9.27	8.679%	$10.0745	$10.07	$10.05	$10.10
Purchase #4	$218.83	10.347%	$241.4723	$241.47	$241.45	$241.50
Purchase #5	$57.75	7.258%	$61.9415	$61.94	$61.95	$61.90
Purchase #6	$137.53	11.840%	$153.8136	$153.81	$153.80	$153.80
Purchase #7	$55.72	7.180%	$59.7207	$59.72	$59.70	$59.70
7 purchase totals =	$528.07		$580.2699	$580.25	$580.15	$580.20