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	$36.39	10.723%	$40.2921	$40.29	$40.30	$40.30
Purchase #2	$108.96	6.769%	$116.3355	$116.34	$116.35	$116.30
Purchase #3	$19.95	3.670%	$20.6822	$20.68	$20.70	$20.70
Purchase #4	$144.72	11.815%	$161.8187	$161.82	$161.80	$161.80
Purchase #5	$68.75	13.477%	$78.0154	$78.02	$78.00	$78.00
Purchase #6	$84.78	9.282%	$92.6493	$92.65	$92.65	$92.60
Purchase #7	$88.38	10.418%	$97.5874	$97.59	$97.60	$97.60
7 purchase totals =	$551.93		$607.3806	$607.39	$607.40	$607.30