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	$25.93	13.685%	$29.4785	$29.48	$29.50	$29.50
Purchase #2	$188.82	11.103%	$209.7847	$209.78	$209.80	$209.80
Purchase #3	$147.29	4.570%	$154.0212	$154.02	$154.00	$154.00
Purchase #4	$47.27	13.577%	$53.6878	$53.69	$53.70	$53.70
Purchase #5	$165.35	4.496%	$172.7841	$172.78	$172.80	$172.80
Purchase #6	$10.75	5.511%	$11.3424	$11.34	$11.35	$11.30
Purchase #7	$83.49	11.169%	$92.815	$92.82	$92.80	$92.80
7 purchase totals =	$668.90		$723.9137	$723.91	$723.95	$723.90