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	$24.31	3.281%	$25.1076	$25.11	$25.10	$25.10
Purchase #2	$180.88	5.848%	$191.4579	$191.46	$191.45	$191.50
Purchase #3	$9.86	12.497%	$11.0922	$11.09	$11.10	$11.10
Purchase #4	$56.29	5.353%	$59.3032	$59.30	$59.30	$59.30
Purchase #5	$18.49	4.675%	$19.3544	$19.35	$19.35	$19.40
Purchase #6	$132.31	3.461%	$136.8892	$136.89	$136.90	$136.90
Purchase #7	$172.55	4.246%	$179.8765	$179.88	$179.90	$179.90
7 purchase totals =	$594.69		$623.0810	$623.08	$623.10	$623.20