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	$106.90	8.617%	$116.1116	$116.11	$116.10	$116.10
Purchase #2	$112.45	5.313%	$118.4245	$118.42	$118.40	$118.40
Purchase #3	$221.75	3.777%	$230.1255	$230.13	$230.15	$230.10
Purchase #4	$111.87	7.182%	$119.9045	$119.90	$119.90	$119.90
Purchase #5	$56.77	4.711%	$59.4444	$59.44	$59.45	$59.40
Purchase #6	$36.50	8.106%	$39.4587	$39.46	$39.45	$39.50
Purchase #7	$135.82	6.297%	$144.3726	$144.37	$144.35	$144.40
7 purchase totals =	$782.06		$827.8418	$827.83	$827.80	$827.80