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	$36.78	3.588%	$38.0997	$38.10	$38.10	$38.10
Purchase #2	$139.76	6.715%	$149.1449	$149.14	$149.15	$149.10
Purchase #3	$91.52	11.527%	$102.0695	$102.07	$102.05	$102.10
Purchase #4	$171.72	7.151%	$183.9997	$184.00	$184.00	$184.00
Purchase #5	$42.41	6.579%	$45.2002	$45.20	$45.20	$45.20
Purchase #6	$99.40	12.295%	$111.6212	$111.62	$111.60	$111.60
Purchase #7	$70.81	11.384%	$78.871	$78.87	$78.85	$78.90
7 purchase totals =	$652.40		$709.0062	$709.00	$708.95	$709.00