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	$25.35	3.131%	$26.1437	$26.14	$26.15	$26.10
Purchase #2	$230.80	8.545%	$250.5219	$250.52	$250.50	$250.50
Purchase #3	$248.44	13.307%	$281.4999	$281.50	$281.50	$281.50
Purchase #4	$144.86	7.229%	$155.3319	$155.33	$155.35	$155.30
Purchase #5	$116.60	12.479%	$131.1505	$131.15	$131.15	$131.20
Purchase #6	$103.81	10.446%	$114.654	$114.65	$114.65	$114.70
Purchase #7	$145.61	4.250%	$151.7984	$151.80	$151.80	$151.80
7 purchase totals =	$1,015.47		$1,111.1003	$1,111.09	$1,111.10	$1,111.10