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	$38.76	4.779%	$40.6123	$40.61	$40.60	$40.60
Purchase #2	$175.78	11.644%	$196.2478	$196.25	$196.25	$196.20
Purchase #3	$139.70	4.416%	$145.8692	$145.87	$145.85	$145.90
Purchase #4	$10.31	11.851%	$11.5318	$11.53	$11.55	$11.50
Purchase #5	$15.69	13.487%	$17.8061	$17.81	$17.80	$17.80
Purchase #6	$58.87	9.841%	$64.6634	$64.66	$64.65	$64.70
Purchase #7	$184.53	4.130%	$192.1511	$192.15	$192.15	$192.20
7 purchase totals =	$623.64		$668.8817	$668.88	$668.85	$668.90