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	$90.56	13.427%	$102.7195	$102.72	$102.70	$102.70
Purchase #2	$111.77	7.339%	$119.9728	$119.97	$119.95	$120.00
Purchase #3	$19.27	10.332%	$21.261	$21.26	$21.25	$21.30
Purchase #4	$238.62	12.109%	$267.5145	$267.51	$267.50	$267.50
Purchase #5	$105.27	12.426%	$118.3509	$118.35	$118.35	$118.40
Purchase #6	$78.35	9.845%	$86.0636	$86.06	$86.05	$86.10
Purchase #7	$76.28	8.348%	$82.6479	$82.65	$82.65	$82.60
7 purchase totals =	$720.12		$798.5302	$798.52	$798.45	$798.60