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	$83.86	9.141%	$91.5256	$91.53	$91.55	$91.50
Purchase #2	$223.86	12.646%	$252.1693	$252.17	$252.15	$252.20
Purchase #3	$52.65	7.142%	$56.4103	$56.41	$56.40	$56.40
Purchase #4	$127.97	3.523%	$132.4784	$132.48	$132.50	$132.50
Purchase #5	$54.26	10.173%	$59.7799	$59.78	$59.80	$59.80
Purchase #6	$18.48	13.716%	$21.0147	$21.01	$21.00	$21.00
Purchase #7	$35.92	11.746%	$40.1392	$40.14	$40.15	$40.10
7 purchase totals =	$597.00		$653.5174	$653.52	$653.55	$653.50